Can't say I really follow what was going on there.. As far as:

Game win scores from gold I (+10 per win was not guaranteed, as if I was in diamond)

This will always happen when your rating is above the league rating range, so in Gold 1 against other Gold players there's no score bonuses for scorestreak etc above 2799. If that was posed as a question and not a statement? :)

Rank referring to diamond III (336 in diamond)

Seems that once you go up a league you are always included in that ladder, even if your CP drops 🤔