Subtle Word Choices
There are some word choices in the article that I find intriguing - not surprising, though.
Right out of the gate, the author describes Tueller's research as "a rudimentary series of tests." I am not familiar with his actual methodology, but the wording of the article certainly seems intended to undermine the validity of his conclusions. By calling them rudimentary, the implication is that the tests were non-scientific and results, therefore, non-valid.
Later in the article, the author refers to "the 21-foot rule and other axioms that have emphasized how to use force, not how to avoid it." The word "axiom" is interesting here. It implies that these concepts are considered to be self-evidently true, rather than proven through objective testing. Again, there is a subtle linguistic push here that seems to be intended to undermine the validity of the training the author is calling into question.
It's subtle, but I see these things as a form of ad hominem attack on the proponents of the current police training standards, rather than a legitimate argument against the standards themselves. This is definitely considered dirty pool in debating circles.