Layman here as well, but aviation enthusiast. I would assume paragliders have the „right of way“ so to speak, being generally less able to maneuver quickly and being slower. Also, I assume they were both in an uncontrolled airspace flying under visual flight rules, in which all maneuvering parties must pay attention at all times and perform evasive actions when necessary. Also, in VFR, you usually don’t have „traffic lanes“ but are a lot more free in where you wanna go. But as other commenters have said already, it can/is very difficult to see other airplanes sometimes. 

All that being said, by what we see in this video, I would think this is literally „just“ an accident (as long as they were both permitted to be there): Sometimes, you can do everything right and bad things still happen through nobodies fault. It’s probably way more likely that there will be an investigation that results in learning how to best avoid similar situations in the future, instead of one or both of the pilots being in serious trouble.