I can absolutely agree with that. I assume this detailer isn't a fixed shop location (since he was at someone's residence). He would only need to get personal liability insurance on himself as a person, which really doesn't cost much, even if it's covering him during business endeavours. Fixed shop location insurance is much more pricey, but still not so rediculous that it's out of the question.
My comment was more geared towards what I've read in various threads over the past few months. Many Autopians seem to think that if a detailer doesn't carry an insurance policy, then they're a "hack" and are running a "back alley detailing business", which isn't the case at all, IMO.