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What you quoted is an objection that St. Thomas refuted in Reply to Objection 3 in the same Ia. Q. 51 Article 2 :
Although air as long as it is in a state of rarefaction has neither shape nor color, yet when condensed it can both be shaped and colored as appears in the clouds. Even so the angels assume bodies of air, condensing it by the Divine power in so far as is needful for forming the assumed body.
St. Thomas's explanation in the "I answer that":
Some have maintained that the angels never assume bodies, but that all that we read in Scripture of apparitions of angels happened in prophetic visionβthat is, according to imagination. But this is contrary to the intent of Scripture; for whatever is beheld in imaginary vision is only in the beholder's imagination, and consequently is not seen by everybody. Yet Divine Scripture from time to time introduces angels so apparent as to be seen commonly by all; just as the angels who appeared to Abraham were seen by him and by his whole family, by Lot, and by the citizens of Sodom; in like manner the angel who appeared to Tobias was seen by all present. From all this it is clearly shown that such apparitions were beheld by bodily vision, whereby the object seen exists outside the person beholding it, and can accordingly be seen by all. Now by such a vision only a body can be beheld. Consequently, since the angels are not bodies, nor have they bodies naturally united with them, as is clear from what has been said (Article 1; I:50:1), it follows that they sometimes assume bodies.
So although angels cannot "create" matter, they can "assume" body when permitted by God and facilitated by divine power. Article 2 does NOT cover the topic whether angels can create/ destroy matter, so we cannot use it to argue either way.
Aquinas's physics is based on Aristotle's physics, which is outdated and worthless now. Therefore we read Article 2 as simply an affirmation that angels can assume body when God allows. How this angelic apparation interacts with modern law of physics is left unspecified.
But as a general rule, Christianity believes that only God can create / destroy matter. So if an angelic apparation requires creation / destruction of matter, it's not the angels who do them, but God. Although God can suspend laws of nature on a case by case basis (making it a miracle by definition) He may not need to do so to make an angel appear to us.