It took me some time to realise what was happening exactly :P

First, he walks against the way the stairs are moving. This takes 180 steps.
Second, he walks with the way the stairs are moving. This takes 120 steps.

That means the movement of the stairs is (180-120)/2 = 60/2 = 30 steps.

As the speed of the stairs disappear, the amount of steps to walk down is 180-30 = 150.

So it is 150 steps :)

And at home he had most likely eaten some donuts.