I suspect that's what going on is this:
- There is an metallic flavor in the canned meat
- Browning the meat either reduces that flavor, or masks it with other flavors
Steaming, poaching, or other water-based cooking method isn't going to allow it to come to a sufficient temperature to brown it. Grilling or frying (in oil) will cause the Maillard reaction (protein browning) which creates new chemical compounds.
If you have a microwave, try heating up a slice in there, as I suspect that it'll still taste metallic. If you don't have a microwave, you could try steaming it, or just sampling it at room temperature.