
The thing is that what people above here are saying is that there is no such thing as a 'total top' or 'total bottom'. There are stereotypes in manga that are associated with one sexual position and you are used to seeing those and that's fine, you shouldn't be blamed for that. But in real life it's not because someone is domineering and tall that he will always want to only top guys if he's gay. I also think that many people in love will change (sometimes unconsciously) for their lovers and do things to please them, so even in that way the 'change' you notice here is not that unnatural.
But mc isn't 'a total bottom' anyway, since he tops again later on. You're just seeing his cute sides now that he's in love, which is pretty realistic I think.
So the wolf dude is a bottom now is it just me or does that seem a bit out of character