You handled the situation very well. In my opinion, messages like this are spammy. I rarely get "serious" discord DMs, it's often people just dropping a link or a copypasta to dozens of people.
And you weren't too mean: if this person was being annoying or too pushy, it's your right to tell him to stop (in a nice way). It's his fault in the first place !
RE: Several Steemians have been REACHED AND ASKED FOR STEEM by DMing