RTFA. Hell, read the fscking summary: "... compared to healthy sperms stored for the same time in the same temperature away from the computer."
Except that they method they used to maintain temperature didn't involve a laptop in the control area; they attempted to cool the sample kept near the laptop by an air conditioning system. This would introduce significant vibration, a temperature gradient, and potentially alter CO2 and O2 concentrations near the sperm.
It's not like running this control would be difficult, so one can only guess why they didn't bother to do it.