I've seen some people use 10k between gate and ground, to make sure it really is low and not just floating.
As far as I understand it, the output pin is pulled low on the Arduino, so that should not be needed?
Completely unnecessary... but I'll admit that it can't HURT.
That's for safety, not some electronic engineering reason. It's there so the transistor doesn't switch on before the Arduino program starts running (who knows, the Arduino might even fail to start...)
If you look at the original post, I highlighted a line in blue and that's what I commented on... the fact that a 100 ohm resistor in series with the Arduino and MOSFET gate "couldn't hurt". I was not talking about the 10K pulldown.