The transaction that sent out your bitcoin was made barely seconds after it was received, so most likely there was a script running (probably on your PC) that sent the bitcoin to the attacker's address almost immediately, and also overpaying in fees (88.7sats/byte while the average on that day was ~15 sats per byte).

Like the posters above have said, either your version of electrum is malware, or your computer has been compromised.
Run a complete antivirus scan to find out.