Well to me, if they follow what you said and this particular store only feeds one pinky per month, that qualifies as intentional starvation to me. Because they're too lazy or don't care enough to do the research to feed the snakes properly.
But yes, that one on the top does look very underweight. Maybe go back there and ask them why that one is so skinny and/or if they're having a hard time getting that one to feed before you create a petition.