As the Tor Project itself already notes in its reply, it's not feasible "to try to imitate normal SSL certs because that's a fight we can't win (they will always look differently or have distinguishers, as has been the case in the pluggable transports arms race)."
Even if the certificate is valid, there are lots of other distinguishing factors. You can go as far as timing attacks. As the answer alludes to, they have an entire project around obfuscated transports primarily for clients and private bridges. [1]
But there's no need for obfuscation here as the ORPort can 'simply' be closed, if it wasn't such a hassle to actually implement.
Even if the certificate is valid, there are lots of other distinguishing factors. You can go as far as timing attacks. As the answer alludes to, they have an entire project around obfuscated transports primarily for clients and private bridges. [1]
But there's no need for obfuscation here as the ORPort can 'simply' be closed, if it wasn't such a hassle to actually implement.
[1] https://gitweb.torproject.org/torspec.git/tree/pt-spec.txt