He spent a month in a hospital as a small child. Of course this impacted his autism. We know that social interaction, play therapy, etc can be effective at reducing the severity and impact of autism and this is the direct opposite. How do you think a small child is going to learn about social interaction if they're stuck in a hospital without as much interaction and with much of the interaction being to the point? They're likely bored and witnessing the dry, clinical interactions of many of the staff. Neither of which are helpful.

Even staying a few days as a toddler is highly impactful on normal kids. They often don't understand why people are hurting them (IV, blood draws, ecg stickers, etc). They hate being stuck in the bed or their room for days with just toys and screens to play with - no running of course. In my experience it seems that fears and nightmares are common. The way the kid interacts can change for a short time after getting home (not as interested in the same type of play as before, happier with screen time, not as trusting of others, etc). Staying in a hospital is rough for someone who is fully developed and knows what's going, it's way more impactful for those who aren't.