They have never come out and said there was this specific incident at this time with this thing. But we've been putting two and two together and we're all pretty good at math here.
What we know:
J$ was probably a little over a year when Jenn showed him eating whole green grapes while Tim rode Rise of the Resistance.
Shortly there after and from then on...J$ was only hand fed little teeny tiny bits of food. Like a baby bird. Sadly, I'm not exaggerating.
Jenn left little bits of J$ saying things about choking hazards in videos. Specifically when he told someone at Trick or Treating that a Starburst is a choking hazard. There were several others. He can't have popcorn at 4 years old because he could choke. There were a bunch.
In the very last live video, on Tuesday or whenever, Jenn was asked about baby led weaning for Da Baby. Jenn replied with, they are taking it slow, because choking is very scary. J$ choked a few times when he was doing baby led weaning. Not exactly what she said, but close to that.
So we called it way back when his feeding changed that he choked. Now Jenn has confirmed it. We do not know that it was for sure a grape, but we've seen the kid eating whole grapes at a far too young age. It most likely was a grape on one occasion.