Surely the implication is that when you 'burn whatever is behind that UserID' you would delete the records of who DeletedUser4510 was friends with (and who was friends with DeletedUser4510).
If all you do is rename someone to DeletedUser4510, you pretty obviously haven't deleted all the data you hold on them.
If all you do is rename someone to DeletedUser4510, you pretty obviously haven't deleted all the data you hold on them.