That sounds like a logical explanation, Galvanized steel though, wouldn't be my choice for a squirrel guard. Usually those things are inverted the other way though, with the large size of the pan fanning to the outside, maybe it was modified and put up by someone that didn't know how to install it. . My next guess would of been something involving a grain silo. Don't have good enough pictures of the find, location, or backstory.
I think I am going to go with my original idea, The metal and ridges and the way it was modified. Usually those squirrel gaurd are made of stainless and inverted. The galvanized metal would of been more than enough for squirrels to get a grip, plus it rusts, probably wouldn't of been used for any "cable" power or phone line used by utilities.
I think I would go with one mans attempt to build something to keep the dust out of coming down the stove pipe during the dust storms of the 1930's. Most likely didn't work.
Dust Bowl era Grain Silo vent? Blown off in a storm?
Whatever it was it was laying on the ground for some time, there are roots coming out the the top. probably the most logical explanation.
Must of looked like a flying saucer when that got ripped off that silo roof.