Of course there are various versions of NPCs, some stand and do nothing, others are more complex, they often "adapt" to certain conditions. For example, if an NPC is following the player it might "decide" to switch to running if the distance to the player reaches a certain threshold, decide how to navigate around other dynamic/moving NPCs, etc. In this example, the NPC "acquires" knowledge by polling the distance to the player and applies that "knowledge" by using its internal model to make a decision to walk or run.

The term "acquiring knowledge" is pretty much as subjective as "intelligence". In the case of an ant, for example, it can't really learn anything, at best it has a tiny short-term memory in which it keeps certain most recent decisions, but it surely gets things done, like building colonies.

For both cases, it's just a line in the sand.