I'm thinking this was such an anomaly with definable circumstances (being left alone for 8 hours and drinking all his water!), he just couldn't hold it. I don't think he'll make a habit of it

PS: My girl is routinely left alone for 8 hours at a time as well while the BF and I are away at work. Neither of us live close enough to let her out at lunch. We crate her while we're gone and if she has ever had an accident it was because we left her too long (which she hasn't had an accident in years besides her incontinence but that's a different story).