I have one of those hurtful abusive mothers and I can see that OP was just being nice, repaying a kindness he felt 6yrs ago like he said. You are being sensitive of you can't see that.
Totally see where you're coming from, but I do think it's a nice reminder during quarantine. Time is passing so weirdly now, it's hard for me to keep track of what month we're in, let alone the date.
To me, it’s just recognition that the type of people who frequent this site aren’t always good at remembering this sort of thing. It doesn’t apply to everyone, but I’m sure there are people who saw this and appreciated it.