They’ve used OSM’s “add as friend” function to make you aware of their profile. OSM has not been “hacked”; they’ve just signed up to OSM like any other user might do and used the normal functionality of OSM.
Nothing is wrong with OSM. However, https://www.openstreetmap.org/user/Master%20services shows that this user account does not exist, so perhaps someone reported them to the admins and the account was deleted, or they renamed it.