I heard a line in the movie The Reluctant Fundamentalist
Looks like you picked up a couple of weights, too, huh?
The speaker of this line apparently suggests that the other party has gained weight. But why does he use weight as a count noun? According to the Macmillan Dictionary, weight is a mass noun when referring to a person's heaviness. The character here is not a native speaker of English, but appears to be highly educated (Princeton-educated) and have a very outstanding proficiency. And the actor is an Oxford-trained English actor. Is this usage grammatical?