And yes, it was a silly way to do it. Nothing about the child-sized rescue submarine made any sense in a real-world way. Yes, the thing would have jammed up in the caves. It would have cost time and lives to extract it so the rescue could get back on track. So why fly out to Thailand to try to take over the rescue?
The key bit of information is that the sub was made by the tunnel-boring arm of his business empire. To make his hyperloop a credible project rather than just a vanity project to be used against him in the boardroom, he needed a leap in tunnel-boring speeds that amounts to magic. Drilling fast and removing heat and spoil in water or other chemical medium might provide enough magic.
It might provide enough magic, certainly, if he only needed to convince enough idiots at the top of his organization. Actual progress was unnecessary. He could make do with a stunt. Even better, because he wasn’t allowed to actually fuck up the rescue, he didn’t suffer blame. Then he could blame the little people for not appreciating his vision.
So the incomprehensible shitfit he threw when he didn’t get his way in Thailand becomes more comprehensible. Maybe. It’s all marsh gas and rainbows, one way or another.