Base on that transaction that you posted, and the other guy on Github who's funds were swept in the same transaction, I can only assume that your seed was compromised. Did you sign up for any give-away or stake in some air-drop, or something of the sort? Did you divulge your seed to any entity that promised you a reward of some type?
I never did anything with my seed at all
What about some other wallet software? The fellow on Github who's funds were also stolen mentioned he had installed a wallet on different machine, I'm assuming he means some software other than Electrum. Have you used some other software to access your Electrum wallet, possibly?
It's rather odd, because the other guy was using the Android software, and you indicated you're using Windows Desktop software. The issue gives me the impression that a hacker gained access to your private keys or seed phrase, but to have done so on two separate platforms (operating systems) is rather unlikely.
I encourage you to think back to any risky behavior you may have engaged in that could have led to your being phished.