Among the list of people he transmitted to is his 2 year old grand kid, I don’t think anyone would be careless about this
You say this, but just yesterday my girlfriend’s co-worker was telling her about how get family member was throwing a big BBQ, because the family wanted to get everyone together. She refused to go, and her husband (mind you, they’re both well in the “high risk” camp) was angry all weekend about it.
Turns out the family member hosing tested positive for Covid and is likely to have spread it to the assembled grandchildren and grandparents who “didn’t want to wait a few more months to see their grandkids”.
Never underestimate the human ability to assume it won’t happen to them.
That said, it’s definitely possible this guy had no idea. I just think you can never rule out people just flat out not thinking right. Especially if they come from the US, where we have a president constantly downplaying it all.