My take: he had worked with such cretins before, I think he didn't really want to associate his favorite name with them.
Out of Uni, in the workplace I am legal-name - no more, no less. I don't want work bullshit to taint what I associate with friends and good times.
In further adult life, you get my legal-name until I know you well enough that we're social and you overhear my nickname.
It also means legal-name is more disciplined, whereas nickname is not...
My wife knows when to use which one. :-P
My take: he had worked with such cretins before, I think he didn't really want to associate his favorite name with them.