As quoted from the linked post.
It looks like you’re part of one of our experiments. The logged-in mobile web experience is currently unavailable for a portion of users. To access the site you can log on via desktop, the mobile apps, or wait for the experiment to conclude.
This is separate from the API issue. This will actually BLOCK you from even viewing reddit on your phone without using the official app.
Archive.org link in case the post is removed.
I think the difference is that Top is based on sheer number of interactions overall (upvotes, comments etc) while Hot is what is getting a lot of interactions in the present.
Ha. I managed to post my comment on the wrong post and subsequently deleted it, but thanks for the explanation.