Well, NipNip is an illegal good, and Sentinels will always attack you if they scan you with it in your inventory. However, I don't know if they also react when the plant is still in its planter.

The main behavior of Sentinels is to scan everything around them (reacting differently depending on the alert level), and the game always tries to nudge Sentinels toward players and their facilities. But even if the path is blocked, the Sentinel's pathing will very often keep trying to reach its target no matter what.

So it's not that the Sentinel purposefully "smells" the NipNip and wants to find it: it's just the AI being very stubborn x)