I would not be surprised to see changes to how Salbutamol levels are verified in the future. Clearly there are some flaws in the urine test used presently.
They say a single urine sample cannot show excess so instead looked at the other 21 and determined that in that context the single urine sample was with acceptable parameters
Press release here;
http://www.uci.org/pressreleases/uci-statement-anti-doping-proceedings-involving-christopher-froome/