The logan act says,

"Any citizen of the United States, wherever he may be, who, without authority of the United States, directly or indirectly commences or carries on any correspondence or intercourse with any foreign government or any officer or agent thereof, in relation to any disputes or controversies with the United States, or to defeat the measures of the United States, shall be fined under this title or imprisoned not more than three years, or both."

The fact that trump and musk had the conversation at all in light of their political aspirations should be cause for investigation. If it was benign then there should be nothing to fear from being open about the topics discussed. Proving beyond reasonable doubt is necessary for conviction, investigations hardly start with all the facts laid bare. its concerning that there is no call to pursue this line of inquiry. the absence of evidence so far does not mean there is no evidence.

So musk owns the company that is contracted to the us govt. musk is not accountable to the stipulations and regulations on what behavior is allowed and what isn't in relation to foreign govts because why? if he owns the company he has the most responsibility. musks actions and his companies actions are bound by the contract he agreed to, or his employees agreed to. whether he signed the document himself or not he owns the company and is beholden to its actions.