Sadly, we can't know what do they mean even when they use the seemingly clear term like standard displacement. Because standard displacement had once meant one thing and sometimes it is used to denominate another. It can be either displacement of ship with everything (crew, ammo, etc) but WITHOUT fuel or water. But it can also sometimes be used to replace the term "normal displacement", which is two-thirds of fuel/supplies/ammo etc. OR it can sometimes be used as "loaded displacement", which is ship with full nominal loads of everything, including fuel and water.
So... we can't really be 100% sure. Max displacement or empty displacement figures could be helpful, if they're ever published.
Well whatever "standard" displacement means, it should be enough for us to know that whatever 055's "full displacement" is, it has to be over "above 11,000 tons".