Anit cheat over reacts at times. I have found being kicked by a mod helps :P. Clear lag gets rid of paintings and stuff. The circuits are not even on a clock. It is once a day. The real thing that lags the server in my opinion is all the lava and water griefing the the wilderness.
There are many possiblities. Lag, block glitching, jump boost from beacon. You need proof. Or even more obvious, he hit his friend over. You can hit somoene 2 blocks high and fences are only 1.5
There is actually a plugin that allows bows without lag because it destroys the arrows shot immediately. THat is what they use for OITC and kit PVP. Vote Up with the plugin