It’s actually of mix of both alternate and down. @kiko did a video on it in an effort to try and convince the interwebs that he’s not playing the song wrong… A Megadeth song. The guitarist of Megadeth. With Dave Mustaine within an arm’s reach… 
He kinda convinced me though…
It’s actually another video of Kiko playing that song that made me realize I was playing it with too many downstrokes.
I haven’t seen this video that you posted though. Funny to think that what prompted him to do this was an exceptional amount of comments of people telling him he was playing it wrong 
.
Every now and then we get reminded how insane and/or stupid people can get when sending comments to musicians…
This reminds me of a video I saw a while ago (last year probably) of a guy who experimented playing a selection of Metallica and Megadeth songs and playing them with the James Hetfield way and then playing them the Dave Mustain way (or vice versa depending on whether it was a Metallica song or a Megadeth song). Obviously… You could clearly tell the difference between the two styles of picking (I mean… Clearer than it already his 
… But judging by what Kiko said in this video and the comments he got, apparently some people need that level of clarity)