I think it's pretty clear the guy just rushed through it. I mean, 59 continues and 88 alerts? That's what you get when you just try to run past everything. DmC can also be completed in that time (some can even do it quicker).
So yeah, speedrun's should not be taken as an indicator of actual game length. Your results may vary. --- [INSERT SIGNATURE HERE]
I dont like the parry system and it seems to have a heavy emphasis on parrying. Blade mode seems useless. Boss fight was kinda fun though. --- When coincidence is so convenient, I prefer to call it fate.