New ceiling fan socket with copper wiring
This is not aluminum, but tinned copper instead

There is no reason to use aluminum at such small wiring sizes; what you see instead on such finer-stranded fixture wires is tinned copper.  This is done to allow it to be easily used in applications where it needs to be soldered (say to a circuit board in a dimmer or fan receiver), and has none of the termination issues that actual aluminum wire does.