The IoT system in a widerange ecosystem of connected "smart" devices that can incorporate a verity of smartphone, tablet, wearable devices, vehicle and so on. For this reason, the concept of IoT can be intended as "distributed" or "centralized". The main differences between these two point of view is how you want to model the network you are taking into account.
To answer your question, yes, the IoT can be considered as a distributed system. To confirm what i'm saying, you can have a look at this two papers: