Weak argument + getting called out on your BS = Anger.
When I was a surveyor for the power company, people would ask me questions about my work all the time. Most interactions, even those when I was in someone's driveway or front lawn, were very friendly. Yet, the most negative conversations I ever had were while I was standing on a public road or sidewalk, in broad daylight, because in those cases I refused to present my personal ID. I would show them my company ID, answer every question they had, but if they wanted to see my drivers license or whatnot, sorry bub, no can do. Instant meltdown. But seriously, if I'm not required to show my ID to a cop, then why in the world would I show it to some random dude on the street?
Interestingly, not once did a threat to call the cops result in a cop showing up. I cataloged over 14,000 pieces of electrical equipment in nine months, and only had the cops show up four times, and in those cases I never spoke to the person who called them. All but once the cops never even got out of their cruisers; they just said hello, confirmed what I was doing, and left.
So anyway, yes, that biker had nothing to go on but emotion, and he was perfectly willing to show you.