Effects of sleep deprivation on memory

Sleep deprivation is a serious issue for many adults, and can have profound effects on executive functioning and cognitive performance. An experimenter wants to specifically study the effect of sleep deprivation on memory and designs two different experiments to do so. In Experiment $1$‍, he brings college students into the lab in the evening and has them study a passage. Half of the participants are then randomly selected to sleep in a quiet, dark room for $8$‍ hours. The other half stays up all night reading, watching TV, and playing games. The following morning, the experimenter tests all the participants on their memory for the passage. Table $1$‍ outlines how many idea units (out of $40$‍) from the passage each group was able to recall and how long (in minutes) it took them to take the test.

In Experiment $2$‍, the experimenter replicates the study, but only allows participants in the Sleep Group to sleep for $20$‍ minutes, while Awake Group engages in light meditation for $20$‍ minutes. The results from experiment $2$‍ are also found in Table $1$‍.

Based on Experiment $1$‍, the experimenter concludes that sleep is important for memory. What is a potential alternative explanation for the current results?