This would be no different than any spell that animates an inanimate object. Would you consider a smart phone to be sentient? Come on, Siri can be very humorous! But of course not. It merely accesses information available to it from the world around it. Talking to trees is no different. Like the example in the episode, asking if orcs went by, they leaves tracks, damage the fauna, cast aside chicken bones, etc, all impressions left on the environment. The spell presents the information through the tree, the conduit to the environment that the druid uses. The method of presentation is all part of the druids subconscious.
My opinion of how spells like that work. Of course Treants are different.