Index Card Word and Character counts are context sensitive, meaning they will update depending on where you are in the app, and what action you're taking.
Main Screens (Grid, Outline, Column Views)
The counts are the total of all cards in the project you are currently viewing, based on the contents of the cards' body text.
Card Edit Screen
The count is indicative of whatever field you are editing. If your cursor is in the synopsis field, it will update with synopsis count. The same is true for title, body, and notes.
If you select a range of text, the count of the selected text will be displayed.