Huh.
I had no idea Marvel Groot was that old.
That seems to make it more likely that it’s not a coincidence though, particularly since while Marvel Groot existed, he was still very obscure. I can see Moorcock slipping the line in, and even giving the character that name so he could slip the line in, just for a bit of amusement.
The only thing I don’t like about the fediverse is the constant stream of people blathering on about how “we” supposedly need to centralize and homogenize it and fill it up with botspam, so that easily confused morons with short attention spans will move here.