As far as I can tell the clearing of the camp happened months before this and was not even initiated by either wal-mart or other company that apparently did some clearing as well.

They also would have needed zero permission to clear the camp if they wanted to. Wal-mart could have, at any time, notified the people in that camp that the were trespassing and then either had them arrested or had them formally evicted depending on how the camp fell within state law residency.

This seems to me more like they just figured that once they left, if the land was cleared they wouldn't come back, and the clearing was only illegal for environmental reasons, not anything related to the camp.