[Dafni]

Welcome. And it's not necessarily a BL related phenomenon, you find this everywhere. Sudden lack of cooling/airflow, while more heat is traped or stored inside a body. Nitro engines are another example. When you measure the temp on the head directly after a run, shut it off and wait a moment, the actual temp on top of the head increases a bit.
In E motors this effect might be more drastic, because our magnets and windings store a lot of heat energy. (relative high effective heat capacity)