What he's saying is this:
A block will impede a roll.
Shapeshifting doesn't require a roll, therefore, it can't be blocked.
That said, if it makes sense, If someone uses Intimidate to put up a block (to scare the person enough that they won't shape-shift), I'd allow a discipline roll to beat the block.(since discipline is the default save against intimidate)
That's artificially putting a roll on something that normally has no roll.
The example with mist form and a force-shield is an athletics roll vs a movement block.
I was actually looking through the uses for fate points today while I was on my phone and I saw that paying a fate point can add +2 to to a roll you usually wouldn't roll, I need to find the reference so I can be sure
