Upvote:5
I'm afraid you can't see the Inselsberg from anywhere on the A73 near Coburg. Contrary to JonathanReez's answer, the horizon is not the right choice when using heywhatsthat. Your have to choose the default map showing all parts of land that are actually visible (reddish) I marked those red spots east of the freeway as well as Coburg.
So you see that there are two mountaintops to the east of the A73 south of Coburg from which you can see the Inselsberg, but not from the A73 directly.
This means you saw some other mountain.