His help WAS going to be useless (mostly because Musk's design completely failed to account for the cave geometry) and of course it was a publicity stunt. There's a team of international cave rescuers and medical professionals on scene, but what do they know? Musk literally announced his "plan" to the media before anyone on scene. That's the definition of a publicity stunt.

Oh, and if you just called me a pedophile to the world, WHILE I've been up for 30 hours straight coordinating a cave diving rescue, and the media keeps asking me "Why not Musk's submarine?", you know what, I'd probably say something a lot less polite than "he can stick it up his ass".