Direct DM without following?

Sorry if this is a noob question but I just have never seen it before. I log into one of my ig accounts today and check the dms I noticed I got a dm from what looks like a typical affiliate page but the thing that threw me was I don’t follow this account and I never had conversations with them yet they were able to send this dm direct to inbox instead of getting sent to requests like all my rest. How is this?

This shouldn't happen actually , unless you follow them , Their Dm will appear in message request section.

Probably some friend's account got hacked and everything in the profile may have been edited before sending messages, maybe.