That's my understanding, yeah, when the main clock is stopped,, they can stay choosy about whether a transition is rising or falling while most pins can only wake on "change" or level, not specific direction of change.. It's like this on all new parts since the 2016 revolution.
The fully async pins' low level int can also be triggered by pulses shorter than one system clock, there is no 3 clock cooldown after reti before it can retrigger - Not sure how that works exactly. The datasheet does provide a side-by-side comparison of the two types of pins in either interrupt or port chapter.
Being able to detect ultra short pulses sounds great, until you realize that noise from the environment causes spurious interrupts on async pins 
(of course the usual countermeasures work, they're just more sensitive. also if a pin is connected to nothing and you set it to pull up and enable low level int, it can and often will trigger immediately, while a normal pin usually won't (This was discovered empirically with a pin being used as ersatz reset on tiny 0-series. normal pins worked, using an async one it would sit there continually resetting itself.)