I hope that was at a conflict zone. I had one this morning as well. In a conflict zone, so a completely legit move. I had seen him on the opposing side but left him alone until he fired on me. I stripped his shields and took his hull down to 60% ish to give a hint but let him run.
A few minutes later I was invited into an impromptu wing which was great fun. Took me a while to remember that everything is shared in a wing as I was being careful not to kill steal.

There was also another commander getting in trouble because they were not choosing a side - reminder to all to choose a faction in the conflict zones to declare allegiance and gain combat bonds for kills. This CMDR was taking a few pot-shots at some other CMDRs but I think it was a case of not knowing about how to declare for a side, rather than flouting the groups policy.
All in all, it getting more and more fun out there
