It's still incredibly error prone and just bad practice. It's a telltale sign of a bad developer because a good dev would instinctively just use var without thinking about it. Good devs may make a mistake here or there but this is clearly well beyond a forgotten var keyword.
I'm just guessing, but the site was probably not developed by a technical team, probably some web shop that specializes more on the design/layout/content side and not on the JS side.
So it's likely it's the work of a non-developer than a bad developer. The net result is the same (bad code) but the distinction is that the code was possibly written by someone who wouldn't even be considered a developer.
