The scientific article referred to in this story is here. It should be noted that the amount of disinfection by-products is strongly influenced by the bather load so residential pools have far lower DBPs than high bather-load commercial/public pools.
They just mean organics which pretty much implies that they have carbon, but are distinct from inorganic carbon such as carbon dioxide or bicarbonate. The organics that cause the most trouble are ones that contain (reduced) nitrogen since chlorine often binds to the nitrogen sites (replacing hydrogen) and can oxidize such molecules to disinfection by-products (DBPs) that are volatile, irritating, and or mutagenic. The organics in sweat, urine, skin, etc. would all qualify. Generally speaking, the chloramines that are produced, especially nitrogen trichloride, are the most irritating to the lungs while the trihalomethanes (THMs) that are produced, such as chloroform, have a cancer risk though it is the bromine compounds that are riskier at lower doses (bromoform and especially dibromochloromethane and dichlorobromomethane). I write about various thresholds and risk values (based on EPA data) in this post.
I just purchased the paper and note that were 9 pool types measured -- one was just tap water, one was a hot tub, 6 were indoor pools and only one was an outdoor pool. As was typical with these studies, though they measured Free Chlorine (FC), they did not measure Cyanuric Acid (CYA). To get any sort of mutagenic readings, they concentrated the water samples using organics (MtBE and ethyl acetate and eventually DMSO) to attract disinfection by-products while water was removed through rotary evaporation and blown to dryness under nitrogen gas.
In terms of genotoxicity, the indoor pool using BCDMH (that is, bromine) was the worst which is not surprising since the brominated organic compounds are generally more toxic than their chlorinated counterparts. The next most toxic were the indoor cold (77-84ÂºF) chlorinated pools. The indoor chlorinated hot tub was next, followed by two indoor UV plus chlorine cold (77ÂºF) pools and one indoor chlorinated warm (97ÂºF) pool. The best pool was the cold (68ÂºF) outdoor pool and the least toxic was tap water. To put things into perspective, the best pool (the outdoor one) was around 3x as toxic compared to tap water based on the concentrations needed to induce genomic DNA damage while the worst chlorine pool was around 18x as toxic and the bromine pool was over 35x as toxic as tap water.
Unfortunately, there were no measurements of organic precursors in the pools, their bather loads, or their dilution rates. Interestingly, one of the pools they sampled was measured while being an indoor pool during cold weather and opened up as an outdoor pool during warm weather (this was treated as two separate pools in their data). The genotoxic potency of the pool was 5x lower when there was solar exposure and potentially increased volatization (i.e. better air circulation).
Since residential outdoor pools have very low bather loads, the genotoxicity would be expected to be much lower as well, probably approaching that of tap water. An exception to this might be if one were to have minimal water dilution and a buildup of organic precursors and non-volatile DBPs in the pool, though even that would still take quite a long time compared to the much higher bather loads presumably found in these pools.