Most home wiring is copper, and you're not supposed to connect it with aluminum wire using a wire nut (push-in connectors are fine.) The reason being is the aluminum will apparently corrode. Is it safe to connect aluminum wire directly to the terminal screw in an outlet, or do you need to use push-in connectors to connect to a copper wire and then connect that?
You're supposed to connect to aluminum wire using connections listed for use with aluminum wire. There is nothing magical about one style of connector vs. another, you can't say "all X type are ok for aluminum", they have to be individually listed for aluminum.
You also cannot put aluminum wire on common receptacles, get your money back from whoever taught you that, it's dangerously wrong.
There are aluminum wire nuts, but they aren't reliable. The gold standard for pigtailing or splicing aluminum and/or copper wires is **alumiconns*, a mini verson of a mains lug. Like most lugs, Alumiconns are made of aluminum. Turns out aluminum lugs work fine with both wires, copper lugs don't.
Regardless, you don't need to pigtail. You can directly attach aluminum wires to a receptacle with a CO-ALR rating for its connections, meaning it is compatible with both copper and aluminum. These cost a few dollars more, and have weird gray metal on their terminations.