The data on that website has been gleaned from the Forest Products Laboratories and a few other places. The original testing was done in the 1930s. It's just a rehash with commentary.
One horrible omission are the figures for dry Osage orange. Either the testing was not done, or the results were not included in the 1930s reports. To this day, no one has done the necessary tests on what is certainly one of the best bow woods.
As far as the value of the mechanical properties is concerned, it is true that little can be concluded from the numbers that has not been observed for centuries about how certain woods behave in bending. But, not everyone has learned those things by experience. And, if one knows what to look for in the numbers, a lot of time can be saved by not bothering with questionable woods.
Then again, if you like to see a mystery in every tree you look at and like to prove you can make a bow from weak wood, don't try to learn from the numbers. It will take away the mystery.