The screenshot you had, it should be noted, uses a font with kerning applied due to the fact that the characters in the font are not all of a uniform size (m is wider than i for example, but rather than pad the i with additional whitespace to make the font proportional it has had that space collapsed).
This makes the numbers along the final row take up more pixel space than the x's above them. Here I've highlighted 10 x's and yet it only reaches up to halfway through the 8 in the digits below it:
There are approximately 13 x's for every 1-0 range of digits if my eyes don't deceive me.
In addition, pressing the enter key for a new line consumes 2 characters as well (carriage-return and line-feed respectively).
So I think if you were to copy/paste the entire text box into an application like Notepad++ you should find that your 2000 characters can hopefully be accounted for by this.
There is a small problem in that having an attribute with max value of 2000 characters actually lets you enter 2001 into the UI which will result in the 'value too large' error when saving until you remove the final character, but I don't see problems with the accounting aside from that unless you have further detail.