Video: Buck thought Eddie needed a nickname (9-1-1)

I wonder why Buck was so set on giving Eddie a nickname in the 9-1-1 episode Under Pressure (season 2 episode 1)? Especially since Eddie already was his nickname. And not to mention Buck had such an attitude about it. I also wonder when did Buck finally learn that Eddie's real name was Edmundo? Since he didn't know in the beginning and thought Eddie was short for Eduardo.