Could be many things. An F1 for example, often causes the affected ship to fly off at higher than normal speeds, pointing in an odd direction.
One thing to keep in mind when keeping an eye out for speed modders is that it IS possible to have your cruise speed exceed 350 by use of formations. So just because someone is managing to escape/close in doesn't automatically mean that they are speed modding.
Another thing: From what I understand, it is rather difficult to sanction for speed modding via screenshots. Its something that they generally rely on the server to catch. Keep in mind though, I'm in no way an admin, so I may be completely wrong about that.
