Amalgam can also mean, "A mixture or combination of different things" such as "an amalgam of musical genres" or "an amalgam of unsavory dog food flavors", which, since we aren't talking about mercury at all, nor are we talking about any form of dentistry, should have be evident and deducible from the context.

https://www.oxfordlearnersdictionaries.com/definition/englis...

And we very much are talking about an alloy, which is a "metallic substance composed of two or more elements"

https://www.britannica.com/technology/alloy

Lead is a metal. Copper is a metal, a combination of 2 metals is an alloy.

However, you are right, I did overlook that the compound is an oxide, my bad.