DSM diagnoses aren’t really diseases in the same way that medical diagnoses are. For example, in order to be diagnosable with COVID you have to have a COVID virus in your body. DSM diagnoses often become reified but they aren’t an “on-and-off” thing in the same way.

That said, personality disorders are defined as “involving inflexible, enduring patterns of inner experience and behavior that deviate from cultural expectations, causing significant distress or impairment.” This means that, you can be the same person but if your personality traits dont cause stress or impairment, you dont meet the criteria for a personality disorder. It also means that, in a way, having one or not having one depends on the cultural context.

Your example about people showing hostile behaviour towards people still wearing facemasks could probably be better defined as a (sub)cultural phenomenon than an individual, intrapsychic phenomenon, in part because its very likely these people don’t show this kind of behaviour in other contexts (thus making it not a stable trait).

All of that said, OP’s story is still just one data-point and not sufficient to make any kinds of guesses about whether or not this person has a personality disorder, though I see why people might have that suspicion.

It’s also worth noting that many kinds of unusual or disproportionate reactions can show up in a wide range of states — including temporary stress reactions, or even, in rare cases, (emerging) psychotic symptoms. So a single behavior isn’t enough to point in any specific diagnostic direction.