What you did with the 32 was set and reset 4 bytes.
32 = 1 << 5.
So his code is setting / clearing a particular pin, and is identical to your code.
But how does this relate to a DAC???
For debugging purposes. He is trying to try to the code so it flips a pin - to be observed by a scope that signals that the timing portion of the code is working. He can then add the DAC portion of the code.
A fairly common way to build up and debug one's code.