Kind of sort of. It was a misleading study and didn’t fully understand the mechanisms behind sleep. They were devoid of sunlight, but not light altogether. They still used artificial light, which disrupted the degradation of proteins in the circadian clock which normally would signal you to sleep during periods of darkness. They essentially deprived their bodies of sleep by extending the period where the signal to stay up (light) was present. While a 48 hour period can be entrained, biological assays have shown that there is still a biologically maintained free running period of around 25 hours throughout the body. This is present in almost all diurnal organisms (organisms that are active during the day). Nocturnal organisms tend to have a free running period closer to 23 hours. Both of these have been observed in environments completely devoid of all light, and also in blind humans with complete enucleation (lack of eyeballs), who are unable to have any photo reception. The 48 hour period works because it is a natural multiple of 24, and allows some synchronicity with biological functions throughout the body that were determined by the 25 hour free running circadian clock. While we can function under those conditions, and will entrain to that period, by no means is our biological determined sleep cycle specifically 48 hours.