Hello there Mimir. I spoke to the ones involved and saw the logs. While I do think 12 seconds may be a short time in which to respond to their engagement line, I do find it strange that you were sitting dead still near 2 hostiles in a LF.
Not condoning the insta kill, I know it's not cool but you are asking for it by sitting still after a line like that was thrown out. I know from my experience on this server, regardless of area (Not just Liberty), that sitting still while discussing things is never a good idea.
While I do apologize for the disappointing encounter, I do think you should expect hostility in an Outcast, from Xenos, next to one of their bases.