Did Lord Buddha preach not to believe our own minds?

This is related to mental proliferation or papañca - also called reification or objectification-classification. Also, see this answer and this answer.

From Piya Tan's commentary on MN 18 (the bolded parts answer your question, on why not to trust your mental proliferations as being absolutely true):

3.2.1.1 The Madhupiṇḍika Sutta (M 18) gives us a very helpful explanation of the process involving mental proliferation: this is given in some detail in §§16+17, the Sutta's key passages. §16 describes how mental proliferation tenaciously grips us as we unconsciously follow its dictates through our sense-experiences. Essentially, this domination begins any of our sense-experience: when a sense-faculty, and its respective sense-object and consciousness (attention) come together, there is contact (phassa), that is, a sense-experience. This, in turn, generates feeling (vedanā), how we see pleasure in something perceive as being attractive, pain in what is repulsive, and boredom in the neutral. This perception (saññā), in turn, generates thinking (vitakka), and when we think in this way, we mentally proliferate (papañceti). Notice that papañceti is a passive verb: we have no control over such an unconscious process. We simply explode into countless conceptions (saṅkhā) and perceptions (saññā) about the past, the future and the present sense-experiences. We run after the past, conjure up the future, and misconstrue the present, creating our own world of these misfits of thoughts and imaginings. We are being processed by our mental proliferation.

And also:

3.2.1.3 Mental proliferation (papañca) works hand in glove with how our sense-experiences, how we sense things. It is rooted in our unconscious mind, that is, the latent tendencies, so that we are not aware what is going on: we are deprived of our free will (in fact, we do not have it yet). The full term for mental proliferation (papañca) is papañca, saññā, saṅkhā, which gives us the key words for the working of mental proliferation. Saññā, although related to the “perception” of the 5 aggregates, here it is very much like consciousness (viññāṇa). It works like consciousness, basically aware of sense-objects, but it also evaluates and value-add them, "recognizing" them from our past experiences. In other words, we only allow the familiar into our lives, or perceive all or experiences as we desire them, not as they really are Saṅkhā, too, works like our consciousness but we are here attending to the perceptions we have been accumulating. Its only task is that of projecting notions and imaginings: what we desire, what we hate, what we are deluded with, what we fear. This is, in fact, how our “creative” minds work, measuring ourselves against others, creating problems for us, and lurking insidiously behind our thinking, and at the roots of all religions, including religious Buddhism. Mental proliferation, then, comprises of perceiving (saññā) and notion-forming (saṅkhā) or conceiving (maññanā) — is an explosion of mental constructs created by the power of the latent tendencies (anusaya) of craving (taṇhā), views (diṭṭhi) and conceit (māna).

The list of latent or underlying tendencies are found in AN 7.11 (translated by Bhikkhu Sujato):

“Mendicants, there are these seven underlying tendencies. What seven? The underlying tendencies of sensual desire, repulsion, views, doubt, conceit, desire to be reborn, and ignorance. These are the seven underlying tendencies.”

The "desire to be reborn" (bhavarāgānusaya) is translated by Thanissaro Bhikkhu here as "passion for becoming".

"Now suppose that a magician or magician's apprentice were to display a magic trick at a major intersection, and a man with good eyesight were to see it, observe it, & appropriately examine it. To him — seeing it, observing it, & appropriately examining it — it would appear empty, void, without substance: for what substance would there be in a magic trick? In the same way, a monk sees, observes, & appropriately examines any consciousness that is past, future, or present; internal or external; blatant or subtle; common or sublime; far or near. To him — seeing it, observing it, & appropriately examining it — it would appear empty, void, without substance: for what substance would there be in consciousness?

https://www.accesstoinsight.org/tipitaka/sn/sn22/sn22.095.than.html