same thing happened to me, it showed my btc transaction. just change the server to one that is bch. (click network, bottom right, deselect 'select server automatically' then go to server tab and right click on server (with correct height 478562 as of now, i used casharia) and click 'use as server.' then the btc transaction is gone.
Confirmed Electron Cash works using this process. 
I used the same Bip39 seed as my original wallet now empty of BTC but still full of BCH in Electron Cash.