Why wouldn't he just say?
Because generally people are arseholes.
When I worked A&E, if asked, I would just say I worked in Health. If people pushed I’d say hospital work, if they kept going I’d say A&E, but at thst stage I’d be pretty annoyed. If they then asked doing what in A&E I’d tell them clinician and ask them why they are interested, and I wasn’t aware I was having a job interview.
The reason people don’t say is because invariably, on saying this, they will talk non stop about whatever rash they have, expect you to look and comment and will refuse to take the hint that you don’t give a shit. Then when little Johnny skins their knee they will march them over to you - so that you can convince them little Johnny doesn’t need to be rushed off in an ambulance, it just needs a wash, which you don’t need to be involved in, and no, no bandaging from ankle to hip is not required.
One of my kids used to play a sport that was pretty brutal in the senior years, for which it wasn’t uncommon for someone to be bused off from each game. Funnily, most teams had a parent that was from A&E, ICU or something relevant so we had an unofficial roster and we would very happily and willingly assess injuries and start working on anyone who needed it. That is a choice though, completely different to some random expecting medical advice at a BBQ after demanding to know what you do.