Do you share the computer with anyone? If you didn't download a fake Electrum client, the question is who found your seed and how!?
This is a real question, because if more people use this computer, everyone could see the seed that the OP saved as a plain text file.
as far as saving my seed looks like i made a big opsec error. its saved in a text file on my windoes pc and also a text file on tails. the text file on windows is what probably burned me.
If he is the only user of that computer, then someone did it remotely, and one remote access trojan is quite enough for something like that. It would not be strange if someone had control over his crypto wallet from before, but he was waiting for a slightly higher amount of a few $ that the OP had until then.
Also, although it was not mentioned, maybe that seed was not generated by the OP, but it was a way of buying BTC. In addition to the trick of selling watch-only wallets, some sell the actual seed with a certain amount of BTC - and when a buyer at some point sends a larger amount into his wallet, an unpleasant surprise awaits them.