May be possible but at the beginning of the post, I startes with the registration date of the said user. He registered on late 2017 and I doubt anyone would pay 50 BTC to get the VIP rank on this forum. That's why I am confused. I do not any other reason to give such privileges other than the case of Bruno.
Besides two users named above, Lauda is another one with a custom title. Regarding to your statement, I don't see anything wrong with a custom titles for some users. If theymos feels right (no potential compromises) he has his rights to give them a custom title and theymos can take those custom titles down instantly when he want.
Custom titles, username change, there is nothing wrong with them, as I see.
I don't think the OP has a problem with it. as I see it the OP is more like curious and just want to know how they were able to have a custom title without being a VIP member. I also remember Lauda having a "Grumpy kitty" custom title not sure why he removed. it looks good on his profile while being savage to other forum members.
EDIT: just found this thread
Users with Custom Title. according to this thread, you can have a custom title if you donated 50btc or become a Global moderator or an admin but "you don't necessarily have to donate or become a global moderator or an admin to have a custom title and you can just ask theymos nicely."(according to one commenter on the thread)