What to use here? Besides or Despite

When I corrected my friend's grammar in a comment he said

Thanks for correcting me. I guess I need some grammar lessons despite studying for CPA.

I think he was supposed to say besides, not despite.

Grammar has nothing to do with CPA (certified public accounting)

as despite would mean that

studying cpa wasn't enough to prevent him from making some mistake that needed to be corrected

and besides would simply mean

in addition to studying for CPA I need some grammar lessons

Despite makes sense too

but the idea is off

as CPA has nothing to do with grammar