I think the argument here is that, since it can happen 30s later, you could enter your password, look at the screen, lock your screen & walk away, without being safe. Imagine a location where the mobo itself is secure enough to prevent anyone from quickly inserting something, but anyone could have quick access to the keyboard & monitor.

In that (highly contrived) situation, this attack is useful, since all you'd need is a quick thermal pic, no longer recording needed.