The problem being what is being tested from the "bag of weed". A bag of the weed can contain leaves, other bit of trim and stem. It could aslo have countless thousands of trichomes covering a sample that were not produced by that flower.
The potency of camnabis is in the trichomes. It's what gives the bud that "frosty" look. Although large visible trichomes don't always mean stronger, it is a good indicator.
Some of those THC figures seem a bit odd to me from that article. 30% + THC I find hard to believe