I would be more worried but (1) he's in a home - a trail angel has taken him in and I owe them some homemade marshmallows and nice card at the very least - and (2) he has at least one full course of Cipro that he's currently downing. (Cipro: heavy-duty antibiotic typically proscribed to travelers heading someplace with sketchy water.)
If he was laying on the side of the trail someplace I would be on the road already, but it sounds like he's getting good care. One of the bad aspects of giardia is that it takes a week or two for the beasties to show themselves - so who knows where he picked it up.
Updates as they occur.