Yes, it's a stupid tweet. But essentially saying "I could bring this plane down with my laptop hackery" is a statement about security, not about intent.
The guy has bad judgment, but he's not saying anything that should trigger any action against him (they should investigate the basis for his claim, not him as an individual).
If he were to announce to the passengers on the plane, "I could bring this plane down with my laptop hackery", people would be terrified and want him off the plane. They don't give a shit about intent, they just know the guy is talking about being able to bring down the plane they are on.
The issue is that he was hacking the plane. Intent is irrelevant. The reality is he could inadvertently damage an aircraft system while playing around. A responsible security researcher would not put 200 people at risk to do his testing.
The guy has bad judgment, but he's not saying anything that should trigger any action against him (they should investigate the basis for his claim, not him as an individual).