You use that command in Vim to save and exit the file. But as a modal editor, if you're in insert mode, you'll type it into the file as text instead of a command, thus the search here.
It's the method of saving and exiting a text file in Vim. ':' enters command input mode, 'w' writes to disk and 'q' quits the program. These people mistakenly typed and saved it in non-vim-edited text files.
what is :wq ?