Fortunately, a video does need to have a vertical screen resolution to be counted as a short. So landscape/widescreen videos don't seem to be affected there.

But this can definitely trip people up, especially now the maximum length of a YouTube short is 3 minutes instead of 1. If you recorded a 3 minute video on a phone (or other random vertical screen device like a Game Boy/DS/3DS), YouTube will classify it as a short and there's basically nothing you can do about it.

YouTube has been pushing for longer videos for a while now. I believe it has to do with getting more money for ads. I remember YouTube updated their guidelines suggesting creators to create longer videos (10+ minutes for better monetization)

I couldn't find a source (other than my memory) though, the earliest I could find is a reddit post from 2016 https://www.reddit.com/r/PartneredYoutube/comments/4v6bmy/wh...