Hello.
I played today in Worms, and the game has generated me ErrorLog.

My Windows XP sp3

This is no big deal, if some minor glitches or things happen in your game it generates a file called errorlog.txt. Unless you have major issues with the game you don't really need to worry about it.

Errorlog.txt files occur when the games custom exception handler detects the game has entered an unstable state or has performed an illegal action. It is fine that he submitted the error log as it helps to debug what crashed the game.

But as I understand it, his game didn't crash.

When the game encounters an unrecoverable error (situations when you'd usually see Windows' standard "This program has stopped working" dialog), it will generate an error log and minidump, and display the respective error message.

But as I understand it, his game didn't crash.

It can't "generate" an errorlog file unless it's going to crash or the developers left in a command line argument that makes the game randomly generate them.