OP, this advice is gold. you'd be very stupid to ignore it.
to go into more detail using myself as an example, between July and August I gained 8 lb, but also 7mm on my ab skinfold. between August and September, only 1.5 lb gain and +2mm ab skinfold. between September and October (I had finally recovered enough from injuries to be able to squat, pull and row heavy again, and made some diet changes)... 8-9 lb gain and about +3mm ab skinfold.
if I followed that set 2-3 or 5-7 lb weight gain, I don't think I'd be setting PR's every session and finally be too big across my shoulders and chest/lats to wear a medium tee. I'd probably be stagnating while huddling in the corner with a bag of broccoli, trying to stave off fat gain.
you are LUCKY to start off skinny, and not chubby or fat. milk it for all it's worth and go for the gold. read the sticky "how the biggest got big" and go for it.