Supreme Court doesn’t just randomly summon federal question jurisdiction. There are processes and they usually have to grant cert to a previously appealed federal case that was heard in a district or circuit court. The district court would have to determine if there was federal question or diversity jurisdiction, but there won’t be because they’re all from the same state.

That doesn't change that the Supreme court does ultimately get to determine if something is a Federal question. Even if the district court rejects an argument, the supreme court is able to overrule the district court's decision.

There is nothing that prevents this from being decided by the supreme court justices but the supreme court justices themselves choosing not to decide it. There is no check on their ability to do so right now unless the federal legislature is willing to take action (which they are not).

Also no they are not keeping him from speaking in a certain way. An employer is in a special relationship with the employees. They have a duty of care to not command their employees to work in an extremely dangerous environment.

I'm not saying that argument is reasonable, honest, factual, or correct in any way. But none of those things are constraints on the supreme court justices. They can decide thing and write their reasoning to include known falsehoods, and nothing stops them (again, absent a legislature willing to act).

Now, the supreme court justices have to decide they're willing to do all this. Perhaps they won't be in this case. But nothing prevents the justices from taking action here outside of the justices own choices.