When the reset button on a Verizon-provided DSL modem-router is pressed, the walled garden mode resets to on. Your IT department would have to log into a hidden page in the modem-router to turn it off again, as explained in the FAQ page you linked to: How to Turn off the Walled Garden.
Perhaps the DSL modem-router's walled garden mode was accidentally on at one point, but it's now off. Some addresses may be cached in your computer's DNS cache or in your web browser's cache as the walled garden page. Try refreshing the page in the browser, or try clearing the browser cache. If you're using a Windows computer, try going to a command prompt and typing
If it's not cached on your computer, it may be cached elsewhere in your organization's network. For example, if your organization is using a proxy server to cache webpages or a local DNS server to cache addresses, they may have cached some walled garden pages. Ask your IT department about it.