search the web I found several water heaters with Stainless steel tanks
Stainless Steel Indirect Water Heaters(PDF)
Stainless Steel. Indirect. Water Heaters. Standard Features. 316L Passivated Stainless Steel Tank ... single wall coil, Stainless Steel indirect water heater. ...
It also said "Best Offer- Make Offer". May still be an even better deal.
Anyone willing to get the top cut off and clean with PBW or whatever would have a very heavy duty tun for next to nothing. Anyone brewing large batches is expecting a fair bit of work even in just the brew aspect. It could have been from any industrial use, but would able to be reused with proper cleaning technique; it's friggin' heavy stainless.
Even if there was a coil in it, it would add to the value, and would be salvage in hand when the lid was removed.
I've always considered semantics to be little more than wiggle room.