It looks to me more the latter: he "helping his son" by "speaking about engineering" is a written report in a court case.
Quite a bit of framing
You can waffle with "it's not the same part of HN" or something, but honestly it sounds more like a lot of HN just doesn't like anything which might prevent them from offering their opinion in inappropriate contexts, and their mechanism to avoid this is to refuse to let anyone judge the appropriateness of a context.
Big "what's next, a license to toast" energy from all this tbh.
Yes, according to the current law, which is not serving the needs of society well. If an engineer has been working for many years for a company which was not required to have a license, this is already a sufficient proof of qualification and licensing board should not be able to sanction anyone in such case. On the contrary, they should offer a way to obtain a post-factum license either as a result of exam or based on audit of previously implemented projects, and the cost of such license should not be prohibitive, only covering the reasonable share of the expenses of the board.
The purpose of licensing for society is to restrict certain activities only to qualified individuals and businesses to reduce risks of unacceptable damage. This restriction does not imply that a license should be obtained in order to do something, only that there must be a proof of qualification and a license is a sufficient proof. When and how this proof is presented, should not matter, as long as it happens. The law must only create a liability for those people, who cannot present a verifiable proof.
He likely did not as it would be an involved process and may require insurance.
He is not a party in the court case so presumably his testimony is that of an expert witness. Providing expert testimony as an engineer sounds an awful lot like practicing engineering. He is not licensed and he is not practicing under the aegis of a licensed firm. He's in violation of the law.