How is printf() an expression?

I was trying to learn value categories because of an error that I got and stared watching this video by Copper Spice.

They go on to define an expression and as an example provide printf() at this point in the video (screenshot below).

How is printf() an expression? I always thought that function calls aren't really an expression when written by themselves. They are more like statements as my beginner mind thinks of it. Moreover, the definition they provide mentions operators and operands but none can be seen with printf. What am I missing?

The data type that is mentioned is the return value for printf. What about functions that return void?