As I posted before in another thread - Fr. Sretenovic is far from an expert & shouldn't be posting like this on the internet. Personalitywise he's very nice but the facts are that he grew up NO, went to a NO seminary where he was ordained, then went to an independent priest who taught him the TLM. He himself admits that his training was deficient, yet he doesn't go to a traditional seminary for further training for some reason. He's young & inexperienced & under the tutelage of a priest who loves being a one-liner comic in the pulpit - among all his other outside interests.
An illegitimate child will always be known as such, no matter who the mother marries. The mother usually ended up marrying the father, but that's not the case nowadays.