Oof, I hope he's a much better welder than I am. I see that as having a high probability of ruining an otherwise-rideable bike. Unless he's one of those guys who can weld two beer cans together, most welders have no experience with such thin stuff. I mean yeah it started thin, but now it's much thinner around the holes. The hole is where thickness got all the way to zero, but the rim of the hole where you're welding might be only a few molecules above zero. And maybe more iron oxide than steel, there locally at the hole

I would be much more likely to flow some brazing filler over the holes.