Best Farm & Seafood

This is one of those little grocery stores tucked away inside the Chinese Cultural Plaza that specializes in fresh produce. My wife and I have been shopping here for years, but today will probably be the last day we do that.
I bought a bag of bok choy for $ 2.75 and gave the man (probably in his early 60’s) a crisp, new $ 10 bill. He put it in the till of the register and gave me $ 2.25 back. I asked, «Is that all I get back?» He said, «You give me $ 5.00.» «No, I gave you $ 10.00.» «No! you give me $ 5.00! One hundred percent sure!» We went back and forth for about a minute with him getting louder and more vehement by the second. I was so furious. I told my wife, «I’m never shopping there again.» I also told her that in the future when I’m shopping anywhere, I’m going to tell the person to leave the bill out until they give me change. Or perhaps just tell them, as I’m handing them the bill, «That’s $ 10, $ 20» or whatever the case may be.
Do you think it was an honest mistake? I’ve gotten used to people giving me Canadian coins in Chinatown, so I watch the change like a hawk now, but I wasn’t ready for this. My little son was angry for me, too and wanted me to call the police. He was so disheartened when I told him the police wouldn’t be able to do anything.