Drostanolone isn't just a weight-cuting steroid. It's derived from DHT and is highly androgenic & will give you a massiv increase in power/endurance, especially when cutting alot of weight. So IMO it's more likely that he took it to retain his strength while cutting all that weight rather than just as a weight-cutting susbstance.
You have to have experience with these things to know how they work, Drostanolone isn't strictly a diuretic & should 100% be considered cheating.
You can't compare hormones like this to weed or sleeping-pills or any other borderline "cheating" substances that happen to be banned in competition. Drostanolone is alot closer to testosteron than any of those other things.
Drostanolone is baciscly the same ting as DHT. This is what you can read on wiki about DHT:
In men, approximately 5% of testosterone undergoes 5α-reduction to form the more potent androgen, dihydrotestosterone. DHT has approximately three times greater affinity for androgen receptors than testosterone and has 15-30 times greater affinity than adrenal androgens. During embryogenesis DHT has an essential role in the formation of the male external genitalia, while in the adult DHT acts as the primary androgen in the prostate and in hair follicles.