Having worked in a foundry for 25 years my money is that it was made by an employee on the side. I made lots of things this way.
If you had an air cleaner to use as a pattern it is very possible. Put it in a box, fill it with core sand, let it cure, turn it over, remove the air cleaner. Do the same for the other side, clean it up, drill a hole & make a gate for the metal to go in, drill a couple of vents, paste the halves together & pour. Done!

The 2 posts look like part of the gate where it was poured, or it could be vents. It probably should have been ground off when it was made.