Out of Character
Lol. You were definitely fortunate you had the spell and it worked as well as it did. At first I was going to give you all the details with it, then I read over the spell again... turns out sense foes senses hostility, which I wasn't sure was an exact fit. It made perfect sense in the stereotypical demihuman slaughter modules where the bad guys just hate all humans with an undying passion, but was Hamish really hostile?
Turns out, he was, irrespective of the traitor thing. Bad Temper, Bloodlust, and a quirk of "hates magic" set him off the edge pretty quickly, especially when you didn't attempt to hide your spell - just disguise it as something else.
In the end I figured I'd make it clear. You'd picked up all the pieces, and it came down to a GM call on interpretation. I probably wouldn't have given you as much if it been the beginning of a mystery module ("Cast sense foes on Colonel Mustard!") but in this case I felt it was more than appropriate. Again, good work.