Calling it a “cock-up” is probably giving them the benefit of the doubt. The story is already unraveling. They attacked Iraqi soldiers. The soldiers were Shia Muslims. Therefore they called them “Iranian-proxies”. That is a bit like calling English Catholics living in London IRA-proxies.
They did not even bother to find out who fired the rocket. For all we know it could have been John Bolton out in the desert, or perhaps Mossad. So, what did the USA do….they went and bombed the Iraqi army (LOL). I suppose they all look the same to the Americans. And they wonder why the Anglo-Zionists are hated in the M.E. Hence the Iraqi protests against the embassy in the Green Zone. This will not end well.