I read this as "if any area is well-served by standardized tests, it's math" rather than "standardized tests are the best thing to happen to math". Sort of like a honey badger is best served by a snake bite.
The AMS Notices has an interesting article about a mathematician using his sabbatical to teach high school math that overlaps a little bit with this post: http://www.ams.org/notices/201210/rtx121001408p.pdf
I read it the same way as you did, that math is the best-case area for standardized testing. Thus my point: If standardized testing leads to this kind of 'driving out the good' in math, where it's most easily and effectively used to measure performance, what does that mean for less-well-served areas?
The AMS Notices has an interesting article about a mathematician using his sabbatical to teach high school math that overlaps a little bit with this post: http://www.ams.org/notices/201210/rtx121001408p.pdf