Not so. The engine will restart at a point when the electronic gadgetry decides to recharge the diminished battery back up a level appropriate for further use. It is particularly noticeable with climate control doing its work.In fact, if you have start/stop enabled, the car will not turn the engine back on until you press the accelerator.
Have you never been stopped at, say, temporary traffic lights with a long delay on red? I go through a stretch that is time-controlled by temporary (2 years now!) lights quite frequently and my DCT system often, but not always, decides to restart the engine at a point of its choosing. Whenever the ISS becomes a nuisance, I press the off button.