If the thump happens when you apply the parking brake after it's been driven, can you get someone to pull the ebrake while you look around the suspect wheel to see/hear better where the sound is coming from?
I assume the thump happens when you apply the parking brake in a normal (non-violent) manner.
I can think of two possible causes, won't hazard a guess how probably either one is though. The tough part is figuring out what would cause something to suddenly let go with enough suddenness to cause a thump.
One is that the brake cable gets snagged on something, and when you put tension on it, it snaps free, like plucking a guitar string. Seems like you would have noticed such a thing though, and you said you tightened the cable so I seriously doubt there's enough slack to get blown around by wind to cause a snag. But in the hypothetical world, I guess it could happen.
The other is that since you mentioned play between the rotor and hub, and space around the lug nuts, the rotor would slop around if it wasn't clamped in place by the wheel. Maybe the parking brake applies pressure on the hub in a way that would tend to push it off center. After driving, the rotor ends up in a different position than before you drove, and applying the parking brake pushes the rotor in a different direction, and it eventually overcomes the clamping of the wheel and shifts abruptly. I only ever had a base Vibe, (rear drums) but I've replaced front Vibe rotors several times, on those I pretty much had to beat on the old rotors to remove them because they were such a tight fit (and rust welded too). Without loosening any lug nuts or actually driving, try applying the parking brake, then raise that suspect wheel a bit, rotate the wheel 180 degrees, let it back down and try the brake again.
but that's all just guessing at what might be able to cause it