matter to whom?

To the son, it might not matter because an unplanned child has the some right to enjoy life as a planned child does.

To the OP... I would think that it matters A LOT!!! Basically, OP was married. She and her then H made a conscious decision to conceive a child together. The H, now ex H, wants to pretend it did not happen, rewrite their history together redacting his conscious contribution altotether out of the picture, say that he did not mean to have a child with OP (by extension, ==> that OP did not really matter to him as nearly as much as she thinks she did...), and that it was by accident... and he was under the influence anyway and unconscious and unaware of what he was doing, and... the next claim would be that the OP gave him a date rape drug and had sex with him without his conscious, full, and informed consent in order to conceive this poor child. That would be his current attitude taken to its logical extreme -

PAST ...the child was planned by him
PRESENT ...how he wants to tone it all down and dilute the importance of his first marriage by saying that the child was not planned by him and was an accident
NEAR FUTURE ... no, actually, now that he has had a chance to think more about it, no, the child was not an accident, no - OP forced him to donate sperm towards the conception of this child; without being drugged and rendered unconscious, he would never have willingly submitted to even having sex with the OP.

In a nutshell, as I see it, the guy is trying to rewrite his joint history with the OP in order to lessen her importance in his life in an effort to make his life history more palatable to his new wife; it hurts OP, and she is quite entitled to her feeling hurt.

Imagine a guy who cuts an old photograph with his ex to remove her from the picture; same thing but on a grand scale that involves real children.