its somewhat luck, but its rarely all luck, and as such i refuse to label it as such unless it actually is - especially being a home game vs a+ hca. this game is WAY more consistent than most folks give it credit for, i don't think people realize that seble's feedback loop was a massive, massive change, when taken over the course of the game in, in terms of reducing major upsets. so, major upsets are really pretty rare these days, probably far less than they should be. ill stop rambling now but the point is, with the large majority of these kind of posts, there is a serious flaw in the team composition of the more talented team, which means they aren't the favorite they appear to be at a glance, or there is a serious flaw in the game plan, or both, so studious coaches should be seriously reluctant to go with the luck factor.
so, to answer... why in gods name would you run a -3? if you just got caught with your pants down (no game plan), then ok. if not, you need to seriously rethink your approach to +/-. huge mistake, probably justifies the entire scope of the loss just on that 1 issue. you wouldn't be asking why they scored 86 if you'd won by 1, but 86 and 93 aren't really that far apart. also, if you aren't going to game plan, or if you thought -3 made sense, either way, you should have adjusted at half. maybe you allowed it and the sim didn't, i didn't look closely enough to rule that out, but assuming that isn't the case, consider tweaking your halftime adjustment option on +/- as well. most likely the sim would have went -1 which still would have been a poor choice but far better than -3.
the other part is you did get unlucky on fouls, and on FT shooting, which is a pretty significant factor. well, at least in terms of how it contributes to the final score, maybe a bunch came at the end, but that rate of fouling and FT shooting can't really be justified, even assuming a handful came late. that contributes several points as well. but again, your -3 really did not help you on that front, you'd have fouled less if you played a reasonable +2/+3, so part of that, also goes back to the same issue (which is kind of a coincidence but still - i mean, its unlucky they hit a bunch of 3s AND nailed you on fouls, those were independent, but you increased the odds of both with the very poor -3 choice).