I'm a firm believer in not messing with someone else's stuff or set-up. As it's been correctly pointed out it's Crown land but I do still respect an effort made by someone else to get their game. So whenever I find evidence that someone uses a spot on a regular basis, I look to observe from a distance, unless I walk right into the middle of it, as I'm curious as to learn what/why someone set something up and where. You learn or verify something from everything you see. Just don't sneak into the obvious shooting lanes with your next approach - if you go into that area again.
Anyways, if I see a truck parked, I don't go into the woods in that specific area. Trust no-one and you don't want to end up hunting down wind of anyone anyways. Meh, that's just me.