Surely 'going forward' would be scrolling down a webpage? So by that thinking it would make sense for scrolling down to be zooming in. You could also see it like pulling the thing closer towards you.
(Very difficult to unlearn though, I'm not in any hurry for zoom-in to be anything other than scroll-'up'!)
When you scroll down a webpage, do you think of it as going forward? I don't think people think about it that way. They think of it as going down. I think people think of it more in terms of spatial terms than in terms of text reading direction terms.
Also consider if you see a signpost with an arrow pointing to the right. That means go right. If the signpost has an arrow pointing up. That means go forward. Or any map, e.g. physical, or gps navigation software, or videogame in-game map, up on the map corresponds to forward in real life.
(Very difficult to unlearn though, I'm not in any hurry for zoom-in to be anything other than scroll-'up'!)