You didnt give us much info (what server you were flying on, and the exact aircraft type, and if there were any airports nearby), but if I understand you correctly you were flying a flighter jet, at high speed, and were reported.

If this is the case, then you would not have been reported because of excessive speed, because this doesnt happen to fighters. Instead, there is a good chance you were flying too fast in or very close to a controlled airspace on Expert. And that is not allowed. See below:

Continuing the discussion from [Fighter Aircraft Etiquette](Fighter Aircraft Etiquette):

IFATC can, and if needed will ghost fighters racing through their controlled airspace. This can happen even when you are not on an ATC frequency.

I hope this clears it up.