I used to work for a salvage yard, and never lied about what vehicle an engine came from. They could lie, but you would have to think why would they? If it was a lot more money I would suspect it. You could ask to see the truck for other parts, and look for similarities in cut hoses, exhaust, wires, basically anything that didn't unplug, or took too much time to remove. Or you could have a buddy call up and ask for an LQ9, and see if they say that they happen to have one with only 33k on it. Maybe ask for a VIN off if it too for carfax or some other BS. More importantly, I would do a compression and leak down test on it. I would also pull the oil pan, and check some bearings if I were worried. If everything is good, I wouldn't worry. You have to ask yourself, what would you rather have? An honest 33k miles with bad compression, or a higher mile LQ4 with good compression. I am more concerned with a well maintained engine.