I'm a big fan of blocking whenever you want, whoever you want. For those of us with mental health problems, for example, it's vital - I have blocked people because something felt off and I didn't know how to deal with it, nothing more and nothing less.
Try not to take it personally - sometimes people just need to make boundaries that don't always make sense to others. And it's important that we let them do that.
That said, I've also been on the other side of being blocked, and I know it can hurt. One big-ish Medium writer blocked me for telling her doxxing isn't OK, and that the thing she was insisting wasn't doxxing actually was. I tried to be as polite as possible, but *shrugs* - it hurt like hell at the time, because my MH problems mean I take criticisms (and blocking is a type of criticism, really,) hard.
Honestly, I think I would've been hurt with the 'lagging behind' comment - it doesn't necessarily mean you're wrong, it doesn't necessarily mean you were out-of-line, but I personally, if it were applied to me, would've taken it as a major confirmation of several insecurities.
And I think I read the piece from the writer you're talking about... if so, I genuinely believe she was hurt. That doesn't mean anything about you personally - I think she has a lot of stresses in her life and is trying her best, but felt singled out and criticised for something she herself is maybe struggling with.
...I didn't intend for this comment to be this long 😅 Oops!
TL;DR: Block whoever you want, whenever you want, and try to understand that when someone blocks you, it's not as personal as it feels.