I was just watching some guitar covers of my favourite songs on YouTube and this one came across unexpected. I tried to find a search term for it but it wasn't successful; I don't even know what it's called! It's a technique that the guy in the video used on the 1:52 to 1:54 (mins) mark of the video. So here comes the question of whether or not any of you guitarist or non-guitarist know the technique that he did. It would help much more if you can tell me what technique it is and a source to learn it or simply if you are experienced enough, can give me some hints or tips on how to do it.

[video]https://youtu.be/ppqxmDEfAu8?t=1m50s[/video]