3 other possibilities:

1.) It was one of those instinctual things where people respond similarly without thinking about what they heard (ex. Saying “you too” in response to things that don’t make sense when you think about it).

2.) He did misinterpret what you meant but he’s not actually interested and just said “same here” to be polite instead of rude (did he ask you for your number, snap, etc. after you said you checked him out? If not, this scenario could be the case). In this case, he might act like nothing happened the next time he comes to the pharmacy for his meds.

3.) He meant that, yes, he’s always checking himself out as well (man is really in love with himself).