I guess, the guys means from this phrase is that the girl is pretty sexy and he is feeling the attraction towards her. About the girl, it depends on the girls and her thinking point of view. It differs with each girl.

Well, exactly what Mayank said. Most girls say that to mean that the guy is hot.

Yes, the phrases means hot. These phrases are generally used by college going students. They just tell to have fun. They do not want to mean anything wrong by saying this.

lol

That phrase may have its origin in the prevailing schema of anything sexual. Don't we simply love licking and "eating" our mates? It usually connotes a physical attraction, both for boys and girls.

Exactly^
Nobody is going to eat you or has plans when they say "yummy"!

lol