From the OP: I thoughtlessly said "oh wow lucky girl" and everyone sort of looked at me, I realised and apologised.
Since I've gotten home 3 separate people have messaged me to let me know said colleague is quite upset at my insensitive comment, and there is nothing lucky about your mum dying - I never said there was!!
I messaged him to apologise but he just replied with "no amount of money will bring her mum back, be careful what you say"
So you apologised as soon as you said it, which should've been enough. At that point everyone should move on, but no.
Then three people sent you the same message. Is that normal behaviour for colleagues? Sounds like he complained to them about you.
You then apologised to him privately, and he still had a go at you - after you'd apologised twice!
I think it was an overreaction on all their parts. Is there some power imbalance here, either officially or socially?
I also think it was crass of him to say how much money his daughter has waiting for her, especially given the difference between that amount & your own property/wealth.
I'm in no way dismissing the pain for the daughter of losing her mum at an early age, but the daughter isn't part of this discussion, so we can all take that as read.
And someone (i.e. your colleague) can have a bad, even a tragic, thing happen to them & it doesn't make them a saint. They can still do the wrong thing. I remember people at work doing practical things out of our own pocket, to help a colleague who needed it to survive after something bad happened to him. He didn't even acknowledge it, let alone say thank you. We just got on with it, & with him.