have I been hacked?

so I got a parse error for this file

class-html.php

now when I went to the file it only had 80 odd lines and the error was it was expecting ( at 81 so no wonder it didn't work.

so... I downloaded a new copy of wordpress and uploaded the class-html and all seems well.

but I can not understand why a file that had 1400 lines suddenly had 80 hmmmm