[Vman455]

The video specifically states that the strakes and their tip vortices separate the flow coming off the rear wheels from the rest of the diffuser, at 7:44. He also says several times (and takes as his initial premise) that the vortices rolling off the strake edges stay at those edges, but the flow-viz patterns in the article clearly show that is not the case; the vortices from longitudinal fences are quite large and attached to the diffuser surface itself until its angle is extreme enough that one bursts, and the chart shows that before that burst angle, these attached vortices reduce lift. The video also asserts that the vortices rolling off an L-shaped vane occur at the tip of the horizontal portion, but images in the article show the opposite--the vortices roll up the opposite side from the L. Finally, the article ends with the explanation that fences in the middle of diffusers are there specifically to generate vortices to improve generation of downforce, whereas the guy in the video says that the fences are there to separate wheel flow from the inward part of the diffuser and that this improves downforce by not messing up the flow, essentially (last two minutes of the video).

Two different explanations, but I don't know which one is correct. Perhaps neither, but one seems more credible to me.