IMO it is all about what they are used to. I've seen them feeding right next to a farm tractor working a field, forestry cutting trees down with chain saws going all day, feeding right next to a busy highway. New and unusual often spooks them. When jogging first became a thing many Deer would bolt in terror when a running person showed up, same with mountain bikes. They eventually got used to it. The downside to any new fad that takes people to the fields and forests, especially in the springtime, is the Doe get scared off the fawns and sometimes won't come back until nightfall, the fawn lays there all day hungry and thirsty.