My guess is that the dog trough must be on the opposite side of the fountain, hidden from view. And I'm afraid my memory is to fuzzy to say for certain about the people part. I would think they'd certainly provide people a spout rather than a trough (LOL!). But I'm not sure whether it is also on a hidden side of the fountain, or whether that's it, just above the horse trough in the middle of that little ledge.
As is hinted at by the picture, Ligonier is a wonderfully quaint little town well worth visiting. And the link I provided to the thread about Fort Ligonier also provides excellent info of other attractions the area has to offer. On a more somber note, this is also in the general vicinity where the Quecreek Miners were rescued and where the terrorists crashed United Airlines Flight 93. If one is in the area, a visit to the memorials would be appropriate.
And, yes. That would make sense so that the poor dogs didn't get trampled by the horses! And the dog and horse owners can drink out of a third side in safety.