Don't realy want to talk about how to bulk up, many people are real specialists here. Actually I have the same problem. I can never gain any (a few pounds sure but not more) weight, but I eat like day and night and I eat healthy food: lots of proteins and vegies.
But since I do breakdancing and Capoeira on the side, I'm pretty toned for a skinny guy. Look like a skinny sh*t with shirts on, but girls who are not necessarily into big guys like it when I go to the pool.
But anyway, that's not the point. The point is: some girls like you big, some don't; some girls only dig tall guys (I used to have a height complex back in high school), some don't. Some like this or that, some don't.
Just like us guys, how do we like girls? Big chest? Big A**? Tall? Petite? Blond? Brunette?
Different people have different tastes.
Don't focus on what one single girl said.