Seems like you have more pictures than are posted in the thread.
Regardless, still a BIG assumption. Lots of equipment in that yard, could be they just tossed it next to the junk truck because they were gonna sell it. I mean, if I took a picture of my garage you might assume I had a GenI hemi in one of my muscle cars. Or that I had a 440 in any of them. Or that my Austin Healey's had been modified for any number of Dodge engines I have sitting around. None of which is true.
Based on the engine mounts and exhaust manifolds, you don't know if that engine was ever in that truck. Maybe they were gonna do it and changed plans.