The accent thing could be viewed as not hiring someone on the grounds of disability. If you can't understand how someone speaks, you can always communicate via Slack or email.

The lunch one - if the argument was not related to work, then I can't see an issue. You don't have to talk personal stuff to the co-workers, so unless the conversation wasn't mandatory and wasn't initiated by the candidate, then no issue here.

Only really valid cause is the firework.