I don’t know enough about ethernet switches to know if this is common. Though, reading their comment again, I don’t really think I’m right about their statement. It’s definitely a light that is frequently designed to be on when packets are still being accepted for waking the computer.
I don’t have a background in CE, but I’ve seen people claim this is sometimes a design used in the past. I think it makes sense that a circuit that is controlled by the computer can be hard wired to turn on both a light and a ethernet port. Though, I don’t know how common this design is in reality.
edit: After searching some, it looks like some port lights can be controlled by a driver. I still think it probably depends on the hardware design though, and this won’t be consistent between ports.
I think driver examples from the Linux kernel are very convincing evidence that the lights can be controlled entirely by software, but I’m interested to see any possible specific port designs where that isn’t true.