When anyone is viewing your usercard on a question, an answer, or on the users list, they may hover over your avatar to produce an expanded usercard that contains extra information. This is also known as a hover card.
An expanded usercard is only available if there are at least 6 characters in the "About Me" section of your profile. When your profile is long enough to show an expanded usercard a drop shadow effect will be shown on your avatar.
This is how the normal/expanded usercard now looks (note that there's no drop shadow effect):
This intentional, but not ideal at the moment. I plan on having a preview card on every user. In my opinion, it's weird UX having it on some users and not all, regardless of a drop shadow or a bio.
As it's intentional behaviour, can the page in the Help center be updated to not refer to a drop shadow that isn't there?