Etiquette

I ran past an older man on the trail today with his dog. I probably pass maybe 15 people a day on this run. About half have dogs. Mostly off leash. I have been running the same trail for like 5 or 6 years. I’ve never had an issue. This guy yelled “You’re welcome!” angrily. I turned around and was like “I’m sorry what?”. And then as you can imagine we had a classy conversation. Anyways I don’t like being rude to people, what is the right thing to do here? Should I yell out “on your left” like a biker? I’m going pretty slow. Should I say thanks or excuse me or both every time I pass someone? Even if there’s lots of room and they don’t have to move? I get startled when people yell “On your left at me”. Sigh I don’t like being chastised by strangers. Not trying to be rude. What is the right etiquette?