The person may have been cheating, there could have been some weird lag between players, where you are showing hits but did not replicate on the other players instance. This game is still in Beta state, so some bugs and issues should be expected. I have not had that happen to me yet, I have seen some shields comeback quicker than they should when the shields are completely down.
In a multi-player game there is one thing that Frontier cannot stop... if a person connecting to the server has really bad connection or high latency there is nothing Frontier can do about that... about the only thing is if they had a certain latency limit like 500 ms then the game could say your connection is not good enough to support Open Play, you need to play Solo mode only until your internet improves.
Also I think if Frontier catches you cheating, and it is 100% proven you should be removed from open play. 1st time for a week, then longer on the 2nd, 3rd strike you are out of open play forever!