That seems more likely to me too. Imagine a fungus that could provide dopamine directly to the brain when a human host meets a certain condition (e.g. a certain amount of direct sunlight, humidity, wind).
Not exactly this scenario, but the psilocybe genus produces chemicals very similar to serotonin.
Agree, it's more like they're responding to stimuli, could we derive somehow that their genes have evolved some degree of ... intelligence?
Eh, I'd say that's a point for debate, but I would argue stochastic survival probability under some prior conditions that haven't changed enough to force further competition.
I mean, apparently toxoplasmosis or something like it can result in personality changes even in humans.