The fallacy refers to the reasoning used to get to a conclusion, not whether or not the claim itself is true. HHDL could very well be wrong, but in order for someone to commit a No True Scotsman fallacy, there must be a particular sequence of events. That is,

1. Claim, like "no Muslims are terrorists"
2. Attack on that claim ("but Osama bin Laden was Muslim")
3. Changing the initial claim by "moving the goalposts" in order to defend it, without seeking to actually address the attack.

All three of these steps must take place for there to be a No True Scotsman fallacy. The fallacy does not refer simply to people wrongly making universal statements.

For example, if someone asked HHDL about Osama bin Laden, he could simply refer to his initial claim that "no true Muslims are terrorists." He may be wrong, yes, and Osama bin Laden being a terrorists tells us that he very well might be. However, because HHDL has not secpfically altered his argument in order to defend it, it is not a No True Scotsman fallacy. That last part is what the whole thing is based on.

It took me awhile to get this too, it is a lot more subtle that it initially appears to be.