This exercise is from the Core Skills section on Pull Offs.

So by now you should be able to play a simple triplet using pull offs. This type of fast playing using triplets is very common in rock solos. Typically a guitarist will choose parts of a scale where 3 notes are close together, and play them in repeating triplets. Just like this example. Here we play triplets from the C natural minor scale - using pull offs for speed.

Moving between strings quickly is something you will need to work at here. As usual, practice it all slowly, so that your fingers learn what frets to play almost automatically. Then work on gradually increasing speed. Another way is to practice getting each individual triplet up to speed by itself. Once you can play the triplet for each string comfortably, then start working on playing them together.

When you have nothing better to do, pick up your guitar and give this little exercise a go. Over time, you'll gain the speed heard in the normal speed audio! Also, try using the pull off triplets to descend fast through other scales - it's a very useful speed technique to know!