EDIT 2: See Hendrik's comments below -- it was due to the three new comments on the question not made by Daniel.
I have 1 favorite change in the dropdown today here on Meta, the tooltip says "1 new answer or comment on your favorites today". So I would guess your says
3 due to (1) the new comments on Greg Hewgill's answer, (2) the new comment on Layke's answer, and (3) the new comments on the question itself; those are the only new actions within the past 20 hours (the current UTC day). But I don't know for sure. Maybe it only counts 1 change per question, so actually 3 of your favorites got commented on or something.
The below doesn't make sense in the context of the screenshot.
The question changed:
edited Sep 15 at 20:26
The favorites page says Sept. 15th, so it's accurate.
3 you saw on the favorites tab was how many favorites that have changed since the last time you looked at the favorites tab, not the number that have changed today.