So anything is possible. Maybe the donation hasn't happened yet in the timeline where theymos updates the donator list.
He
was a donator as far back as 2012.
Not sure if what I am doing is Ok for privacy reasons of the said user, but his name is In there.
It looks like back in the day, users were able to change their usernames or the user might have requested Theymos to change his username after sometime as donators do have such privileges
Look up Blitzboom
It looks like for whatever reason, his display username had changed, a couple of times actually. He has been known as
Nekrobios,
Blitz, in addition to Blitzboom and N12.
Maybe his permissions were set incorrectly when he was "promoted" to donator status?