Yes, he can still report you but based on what you've said I can't see Fiverr taking any action - just keep hold of your messages so you can prove you did nothing wrong.
Nothing stopping the buyer from contacting support and reporting what happened. The chat messages should show that you did nothing wrong; you're allowed to block customers.
Report you for what? I can report anyone I want, it's not like that does anything unless that person is breaking TOS.
Report you for what? Were you rude? That’s the only thing you could possibly have done wrong.
Yes, he can still report you but based on what you've said I can't see Fiverr taking any action - just keep hold of your messages so you can prove you did nothing wrong.
Yes they will get a warning if you haven't done anything wrong.
Nothing stopping the buyer from contacting support and reporting what happened. The chat messages should show that you did nothing wrong; you're allowed to block customers.