You're viewing the page in Safari's "Reader" mode, which is designed for easy reading. To turn it off, press shift-command-R or click the Reader button (white parallel lines on a black background) to the left of the page address.
If it happens every time you visit that page, go to Safari > Preferences and select "Reader" in the left-hand sidebar. Find your site in the list and change its setting from "On" to "Off".