I don’t agree. Using “future Apple Silicon” would have sent the wrong message. And testing code on M2 would make no difference since anything made for M2 will work for M3. We will find out soon enough.
What would be the "wrong" message? That a future product not available until early 2024 will use Future Apple Silicon?
Telling developers to optimize for M2 performance and then launching with M3 doesn't make sense. None of that M3 performance potential would be realized.
Now that M3 is public, Apple could have silently updated Vision Pro description to M3. But they didn't. Do you really think Apple will wait until the last minute to surprise developers?