> You say something is factually incorrect based on your own experiences
Well, yes, a categorical claim that something was "only ever" used by people with certain objective features and for a particular reason is factually incorrect if it was ever used by people without those features or for a different reason, so personal experience, while inadequate to establish that it is factually correct, can be quite sufficient to establish that it is factually incorrect.
(You'll note that while I state that the categorical claim is clearly factually incorrect, that it is also quite likely that, while not a categorical truth, there have been at least some dismissals that fit the pattern that it falsely claims is the exclusive pattern for all dismissals of email as "impersonal" -- the error isn't in saying that some people describe email as impersonal for the particular reason described, but in claiming that that is the only reason email has ever been described as "impersonal" by anyone.)
> then comment on subjectivity
The comment on subjectivity was on a different statement (a claim of what is superior and what matters, both of which are inherently subjective) not the categorical fact claim. Recognizing the difference between subjective statements and fact claims is pretty important to being able to participate in a productive discussion of pretty much any topic, IMO.
They countered an assertion that people that a particular statement about the impersonality of email was "only ever" made by people without access to email by asserting the existence of multiple people they had known to make that particular statement about the impersonality about email whilst possessing an email address. Which would make the former statement factually incorrect even if the second poster's experiences were atypical.
There's nothing "subjective" about logically refuting one sweeping general claim with a counterexample from ones own experience, unless we're getting really postmodern about whether people actually recall others referring to email as impersonal whilst possessing email addresses or just perceive that to be the case...
Are you being serious, or kidding? I honestly can't tell.