Sweep picking uses a picking technique that is a lot different than alternate picking. The main difference is that you don't want the picking motion coming from a wrist or forearm rotation, like in alternate picking.
Instead, you want to keep your wrist straight and stable. As I mention in the video lesson, some people use the term "lock your wrist", which in essence is correct in that your wrist needs to stay in one position. But the term "lock" sometime makes players use a lot of tension to keep the wrist stable. Instead, try to just use as little tension as possible in your wrist to keep it stable.
The actual motion of sweeping across the strings is done by the elbow. If you have the pick balanced over the strings, and not leaning downwards on downstrokes or upwards during upstrokes, both directions will feel equally easy. It feels like your are simply just brushing across the tops of the strings and not digging in at all. I go into this in quite a bit of detail during the lesson.
Also, towards the end of the lesson, I demonstrate a sweep picking exercise that I teach in-depth in the GL365 Academy. I call it "Intervallic Sweep Picking". This method of sweep picking requires extremely accurate timing between the fret-hand fingers and the sweeping motion. I demonstrate this because Andreas mentioned that he can sweep arpeggios patterns where he can have the entire shape under his fingers before the sweep even starts. But when movement of the fingers is required during the sweep, his fingers can't keep up.
I have found that the students of mine that have mastered intervallic sweep picking can pretty much sweep pick anything the want and are also freed up to use any interval combination the want during sweep picking instead of always being locked into the same old major, minor and diminished arpeggio patterns.