To tell ex friend the baby probably isn't his?

[Oofimanoeuf]

An old friend has a child who the friend insisted probably wasn't his. Everyone told him to stop shirking his responsibility and thought it was an excuse. I've stayed in touch with the baby's mum and they just posted about the anniversary of something and said this event was two weeks after she split up with old friend (the day she told him she was pregnant which she stated as the 3rd of January) but I've just realised that the baby was born on the 4th of November... i feel like a terrible friend but the baby isn't actually his is it? Should I tell him I have realised this and try to build bridges? I wasn't one to have a go but we have drifted apart since all this happened as it caused rifts in our friendship group and I didn't stand by him as I felt it wasn't my circus or monkeys at the time.
Aibu to get involved now? Or is it still none of my beeswax?

What were the dates of his leaving party / leaving the country.
Surely it doesn't matter when she says they broke up (she may being dramatic if the event makes a better 'story' on her post) the fact you
100% no is when he left.

42 weeks back from the baby's birthday is 15 Jan so it doesn't sound like it's possible it's his really but surely that's been obvious for ages to everyone else as surely you could all count before now if he definitely left the country at the start of January?