It doesn't look dense urban, things are very often more relaxed in semi rural areas and low density zones; further he has existing underground structures that I would guess have already been approved.
If I had to, I'd bet he's had a conversation with a local planner and had a nod and a wink already.
Which is why these installs usually involve all sorts of external waterproofing, concrete encasement, galvanic/cathodic protections & sacrificial anodes, drainage systems, and interior climate control. They don't just bury the expensive fuselage and call it a day.
Few minutes in and he is mixing concrete: Too much water in this concrete mix. Wrong kind of sand as well... Luckily he seems to have had a professional mix the concrete for the walls, etc.
Tbh I'm not entirely sure I'd trust a partial plane body to have the mechanical strength for the job. In flight the pressure is pushing out not in, and I assume that's what the thing is designed for.
Though the thing is only barely buried so I suppose it doesn't actually have much external pressure to deal with.
He is pouring concrete re-enforcement around it. Biggest issue is during the pour which he seems to have planned in stages to not put too much pressure on it.
If I had to, I'd bet he's had a conversation with a local planner and had a nod and a wink already.
https://www.youtube.com/watch?v=ixh0KIackIk
This is the best feedback he could get to be sure it will run well you YT.
Though the thing is only barely buried so I suppose it doesn't actually have much external pressure to deal with.
https://youtube.com/shorts/nqXgbLjW1ho?si=PmwapHh23zYmIXuh