Sex trafficking on Snapchat

There’s been a lot of talk lately how sec traffickers are making snapchats and adding random woman in hopes that they will add them back and they will be able to see their location

I got a notification that someone added me on Snapchat and I didn’t even add them back but they were still able to send me a message

Their message said “do Ik you”

Like clearly if you have to ask that then no you don’t know me... I can’t help but think it was one of the sex trafficking people... regardless of that I still don’t know them so I blocked them anyway... but I still don’t understand how they were still able to send me a message.. I have my Snapchat on the setting where people can’t message me unless we are both friends with each other and I 100000% was not with this person