In earlier chapters they explained alphas grow based on love in this universe which is kind of a neat concept. That’s why in the main love is an illusion, Dojin (the dad) was small at the beginning (he never loved) and is now jacked af towards the end and in this one (overwhelming love for Heesoo, the mom)
Sieoo loved Byul his entire life which made him taller and jacked when Byul had never loved before in his life, making him smaller.
That’s why a lot of the jokes I see in the comments are people joking if Byul is going to buff up in an instant after falling in love with Siwoo.
(⌒▽⌒)
I’m sure they will use it because they did it with Dojin and they explained it within this manhwa so Fargo kinda set themselves up to do it, giving their reader’s expectations when originally we thought it was because of the artstyle change
If they forget after making a huge thing about it (making Byul self conscious and whatnot because he just can’t find the one and bulk up) then yeah that would be very disappointing. It’s literally a major plot point ( ̄∇ ̄")
Oh yeah I also forgot to mention, here’s another cute fun fact about that concept, but that concept exists apparently because the alphas bulk up to protect their loved one. I think that’s really cute and really plays on the word alpha

Why’s siwoo so jacked at his age compared to byul…. If both are alphas i’d kind of expect them to be built a bit similar