How the chain of command works is the person making the decision takes full responsibility. In this case, it's the President. The function of his advisors is to give him options (i.e. ideas) and present the pros and cons.

There's a lot of conjecture and motivated reasoning from all sides, enough that I'm doubtful that we can know what really happened. So park the actual facts for a moment. Let's just consider the situation in the abstract.

Musk is many things, but I've never heard anyone seriously claim him to have any particular aptitude or expertise around military strategy or conflict resolution. So if Trump is unilaterally executing on Musk's musings, we can derive two definite (and highly conservative) observations:

1. Musk has opinions

2. Trump has dangerously poor judgement