A White Trash Moment

This morning Joshy and I trekked to our local Super Walmart to do our grocery shopping. Jessa was at a sleepover and was thrilled to "get out of" going along. Usually, she is a great help with Josh and I can get things done faster. But today we were on our own.
I promised my little guy a chocolate donut if he could sit nicely in the cart and be a good helper. He was more than happy to comply. There was a fair amount of chocolate frosting on his face and hands when he finished but I had grabbed some extra little tissues so we handled that without any issues. I wadded up the used tissues and tossed them into the back of the cart since the store doesn't seem to have any trash cans out for public use.
We accomplished our shopping chores fairly quickly and headed back outside to load things into our vehicle. I had already buckled Josh into his car seat and had just finished putting the last of the groceries into the back of the van and was glancing around for a cart return stall. As I leaned over to grab the used napkins from the basket, woman walking into the store stopped and asked me if I was done with the cart. I was thinking "Oh how nice! I don't have to stress about walking away from my kiddo in the vehicle just to get rid of this cart!"
But as I turned towards her and said "Yes, thank you! You can use the cart." She made a face and waved me off. "Oh no. That's okay. Never mind." She's sounding huffy and self righteous at this point. And then she walks off looking irritated and maybe disgusted?
So there I stand, confused. Until I notice the chocolate covered tissue still in the back of the cart.
Did she think I was going to leave it in there? Did she think it was something NASTY? I felt completely appalled!! How dare she think that of me?! I'm not some white trash person who would leave some gross garbage in a cart and then OFFER it to someone else!!!
I almost wanted to go after the woman and tell her it was just chocolate on the napkin and that I was throwing the stupid thing away. But how dumb would that be?
So I drove home feeling rather ticked off . But upon reflecting, I guess this will help me to not be so judgemental in the future about others in what could be a simply a bad moment. (But I still hope that woman got stuck with a cart that had a bum wheel......)