explanation says that divide them into 3 groups 5-5-6 and if first two are equal, eliminate them.
I see the point, but why don’t we divide them into 7-7-2. So if first two are equal, eliminate, and only compare the last with 2 blocks to get the result. In this case the least number of weightings will be 2.
Why not?
What if it does turn out that one of the “group of 7” contains the heavier block?
Not sure if this is what led you to think 7-7-2 OP because it wasn’t immediately clear to me either, but the 5 path leads to 3 measurements since you can split 5 into 2-2-1. So it isn’t arbitrary that 6 had the block in it leading to a ‘convenient’ solution.
I think it would be worth it to include it in the video. Perhaps as an addendum or hint under the video as is done in other videos or a link to a complete solution?