Tipping at raves ( am I the asshole)

Hi, I'm sure this has been posted here before but I wanted to share my own experience and ask if I was in the wrong in this particular situation.

first off I'd like to say that I've been a bartender/server for many years and fully understand what its like to be in a tipped employee position.

so the situation was this, we were at a festival last weekend and went to buy some of those little face scarfs from one of the vendors. My husband and I both bought one but we had to ask someone to get us the ones we wanted because they kept them back behind the counter, when we payed my husband didn't tip, after the fact the guy goes "wow if you spent two more dollars you could have gotten a free set of ears, all you had to do was tip two dollars" in a tone that wasn't pleasant and then he stormed off .

I'm sorry but I don't feel like we should have to tip on a retail purchase?!? like all you did was your job that you're already getting paid for?!? Also why didn't he say anything before hand?

we also typically only buy water at the drink stand and sometimes tip but not always. Waters are $7 already and all you did was grab it and hand it to me. Now if we ordered a drink or you mixed me a drink hell yeah I'm gonna tip you, we also always tip our food vendors. But what do you guys think? am I an asshole for not tipping the guy that sold us retail items ? am I an asshole for not always tipping on waters?

Edit : thank you all for the validation! I'm hoping he was just one grumpy worker or was maybe having a bad day but atleast I know that what we did wasn't a jerk move.