The screenshot posted does appear to be legitimate. If you have more than one player type installed (e.g. NPAPI for Firefox/Safari, PPAPI for Chrome/Opera) you'll be notified for each player type. It's quite possible you've updated one player type, but not another. To find out which player types, and versions, you have installed go to System Preferences > Flash Player > Updates tab. Please post a screenshot of the Updates tab.
Thanks for posting the screenshot. The Update Notification you're seeing is for the PPAPI plugin. You have version 126.96.36.199 installed and we released version 188.8.131.52 on Tuesday. The notification will go away once you install the update. To avoid the notification in the future you can opt into background updates, which is the update option 'Allow Adobe to install updates (recommended)'. With this option selected, Flash Player checks for an update daily and if a new version is available it's downloaded and installed silently in the background with no user interaction. Since this is a daily check Flash Player will usually update within 24 hours of a new version being available. With the notification option it can take up to 7 days for Flash Player to prompt that a new version is available for download.