For both of them! Since both of them are aware now, either one could open that ticket. If the maintainer has very specific ideas about how a ticket should look, maybe they can do that themselves quickly, now that they are aware of not complying with the RFC. Then the ticket will perfectly match their expectations.
The maintainer is usually also the one who has to trace the root cause, which in this case the issue reporter did, which is certainly more work than creating an issue according to the formatting and other requirements the maintainer may have. So in that light, the reporter of the issue already did a big chunk of work for the maintainer or the project. I wouldn't really call them acting "entitled" after that. Clearly they put in effort more than could be expected already.
For both of them! Since both of them are aware now, either one could open that ticket. If the maintainer has very specific ideas about how a ticket should look, maybe they can do that themselves quickly, now that they are aware of not complying with the RFC. Then the ticket will perfectly match their expectations.