(1) This is being measured in aggregate. It's no more privacy violating than, say, measuring the amount of non-recyclable trash that ends up at the recycling sorting facility.

(2) Consult the methodology section.

(3) Methylhexaneamine (DMAA, spelled "methylhexanamine" in the article) is the 3rd highest thing in the table. There are several other anabolic steroids in the table (see list below). Chemicals tend to sell under several different brand names and your list may intersect the article's list. It's also possible the article's list just contains a different set of chemicals.

To categorize briefly (the list is heavily steroid-focused):

Aromatase inhibitor (prevent aromatization of androgens into Estrogen): Anastrozole, Clomiphene, Tamoxifen

Masking steroid use: Finasteride (new tests obsolete this, at least for pros)

PED/Weight loss: Clenbuterol

Stimulants: Norephedrine, Ephedrine, Methylhexanamine (DMAA)

Steroids: Trenbolone, Nandrolone, Metenolone, Mibolerone, Metandienone

Weight loss: Sibutramine, 2,4-Dinitrophenol

Also note Table 1, which shows (basically) how quickly various PEDs degrade at different temperatures. Several of them degrade in 0-1 days at 20° or 4°C. So unless a large population is taking them (ephedrine), they tend to drop off of test results.

The other consideration is LOD / LOQ (limit of detection, limit of quantitation) — lower levels here ease detection and measurement.

(4) This study is targeted more broadly at the recreational athlete population, rather than pro athletes.