Check a good descrition of how vex works here https://www.tokeru.com/cgwiki/index.php?title=HoudiniVex
I suggest to start learning and play with more simple setups before diving into something like above. Start from a simple setup to prove idea.
Should be attribute i[]@ then index []
f@element2 = i[]@arr[1];
Also, you can always find useful tips here: https://www.tokeru.com/cgwiki/index.php?title=HoudiniVex
Probably something with cookies or CSS (a:visited), right side is here but it's not showing separation in visited and new topics, it was bold title when new and normal after visiting. Easy to see what you already saw but now all is the same. (I'm using Firefox)
This doesn't give us any information about you issue, show your "not satisfying" result, share setup or example...
The setup from the video is working as expected, tested.
Looks like you're on the right way with flip, do more resolution, add more swirl/turbulence as on ref.
To make it more sandy for render you can try advect pop with amount of particles required for this look or random remove part of particles like 20-30% from flip to make gaps between grains.