Some issues might have to do with the way DNS is resolved by the operating system (the Start > Run \\resource example in the article) and others by the way some applications (like web browsers) do fallbacks for unknown DNS records.
Tangential: I worked at one company that had lower environments end in .dev and they started running into issues when Google purchased (and now sells) .dev domains and one of their project dependencies was hosted in an open source project repo that ended in .dev .. it had fallen out of use at the company and they just trashed the hosted zone, but I imagine at other shops, there's still domain overlap in the wild.