There’s tons of things that trigger dogs. My 4 year old blue healer border collie cross jumped my 1 year old Kelpie border collie cross for getting to close to his food in his bowl that he wasn’t eating. They put on quite a show for a minute or so. The dogs get along great most times. The 1 year old is learning boundaries and pecking order. Not the first time, bet it ain’t the last, but they are together constantly. I don’t do dog parks.
Dad once had a big German Shepherd that was the best dog around people and kids. But let him spot another dog then it was off to the fights. There’s no way dad would have taken it to a dog park even if it was leash only.......