Not great behavior I agree, but what else is there to say other than "it does not match the spec at point 1.2.3"?
I certainly understand the maintainer here, because that’s what I keep telling colleagues at work.
Tickets get really cumbersome if they are not clear and actionable.
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.