Hit head, bite tongue, taste blood. Blood is a bit metallic. Canned tuna sometimes has a metallic taste. I could see how someone might associate that with seafood.
Could also see a jostling of the brain just causing all kinds of random shit to be perceived just due to the brain freaking out for a moment.
No no, I can taste that too, there's no blood or biting involved. Happens when i hit my head really hard, eyes go dark for a fraction of a second, and the taste appears.
How often does that happen that you recognize this? I can't remember the last time I hit my head hard enough that it hurt, let alone hard enough to black out for a second.