but would it be so unreasonable after being followed by some random stranger with a gun at night?

Yea, that's the thing about a gun, the escalation it causes is through the roof ... it's fatal, at a distance ... with that threat you both having nothing left to lose and also, in just about everyone's case, no experience in managing the emotions of that situation so of course you're going to react in some way that might be surprising, unpredictable or even arguably irrational. Merely carrying a gun, and posing the threat of immediate death, is an assault in itself.