Lots of variables. Maybe just luck. But did you try more than once? Maybe your HB didn't proc on your killshot?
I'm level 69 and these were all rank 20ish fights. So my competiton is all near my level or higher essentially. I'm usually fighting teams at level 68 to at least 71, judging from their toon levels. Most of mine are still 64-68.
I check out the stats often before a fight. In the past I look for tenacity in low 30s or less for my targets. Lumi or droids etc. About GS in the mid 40's started to get fairly low yield/high risk. Past two days over the course of 20 matches, my confidence continued to rise and my playing field gradually opened up to include yoda with tenacity up. So basically anyone with a buff, not in the yellow/red, excluding foresight. Yeah, maybe just luck, but I didn't think it could even work against Tenacity Up. My QGJ has been max gear for my level for probably the last week or two; no change. I had him maxed at the last piece of gear that mattered before 70.