Ha, doesn't help that the playing in the audio isn't what's happening in the video which may have been confusing.
There's a lot of string muting. In the intro they mute after every up stroke. But it's a longer down in the intro, when the singing starts it's more abrupt muting.
But from messing around it just sounds like a down up-mute up-down up-mute up-down* strum repeated. You need to do this at a reasonable speed, you'll hear it the minute you do it, if you slow it down it gets confusing hahaha
The down strums are held a little longer, and on the down* you can either mute or do a quick up-down before getting back to the repeated strum
Hope that made sense and helped!