Yes, it is, but the belief - if we take as a given that heresy is sinful, and the Catholic view of the consequences of sin - that priests shouldn't teach the 'orthodox' view defies it even more.
As to whether it actually relies on that belief: there's a good essay by Isaac Asimov called 'The Relativity of Wrong', in which he argues (the parallel with teaching creationism in schools is implicit) that yes, our theories of the Earth's shape and situation are likely to be updated in the future, so they are to an extent 'wrong', but they're less wrong than the belief of the ancients that the Earth is flat. The Catholics would say that the same applies to theology; it evolves over time, so what we've got now is probably mostly right, and anything that purports to re-write all of it is probably wrong, in the same way as scientists would.