Idk Derp: personally I would never tell a skinny guy that I thought being skinny was unattractive. I think whoever says that to you lacks a lot of tact. The only thing I've ever expressed that I find attractive is top knots - but I wouldn't say that to a bald guy!
And I happen to like skinny women, god only knows I've tried to be it for long enough. The thigh gap is just not something I think is attractive. And maybe she's not ana, but she certainly looks it.