It's pretty much been summed-up. The galvanization process is an oxidation retarding treatment done to ferrous metals. Aluminum is not a ferrous metal, and thus needs no galvanization. (Even though it can corrode under proper conditions. It's confusing, I know.)
My guess, which isn't worth any more or less than anyone else's, is that this was possibly a roll of flashing or gutter stock. Galvanized metal is indeed usually "harder" than a like piece of non-galvanized. It's also much heavier than aluminum.
Hope this helps, but you have just about figured all that out on your own. Let me know if you need any more info.
