Probably, but the question is where did you save that text file, on your computer, as a backup to an email or somewhere else? If you saved that file on your computer, there is a possibility that it was opened by someone who has access to your computer (if such a thing is possible), or a much worse option for you, that someone had access to your computer remotely (in which case he still has it).

Try to figure out exactly what happened, and as a precaution, I would personally format the disk and install a new OS - then think carefully about whether you can provide a secure environment for Electrum as a hot wallet on that computer, or is it time to start thinking about investing in a hardware wallet? But even in that case, be careful where you keep the backup and always verify the addresses you use - clipboard malware is a nasty little bastard who made a lot of money to his owners.