This looks pretty complicated but here is a simple way to think about it. After the deltaTime has been added to the accumulator and the physics steps of size dt have been performed, if the physics and display fps are not integer multiples of each other, then some time will remain in the accumulator. This remainder is effectively a measure of just how much more time is required before another whole physics step can be taken. For example, a remainder of dt/2 means that we are currently halfway between the current physics step and the next one. A remainder of dt*0.1 means that the update is 1/10th of the way between the previous and current states.
Yep, he's using DT. Maybe not in the traditional sense, but it's in there. So, yes, it does combine FRL and DT techniques. And if we need to throw in some tweening to keep you happy, we can do that too. ;)