[lucubratory]

They are clarifying that "a friend of mine" is not a euphemism for themselves, because it's more common to use it as a euphemism for yourself than it is to actually talk to strangers online about your friend's life, problems, opinions etc.

[DinaCoder98]

Oh, huh. I now recognize what you're referring to but I never would have realized that without being explicitly told so. Thank you.