Your canvas still drapes much harder than the fabric in the ESB pics. Notice particularly the edge of yours where it's almost creased in on itself, and the drapes make much stiffer peaks. Your cape is actually still after many washes, showing the attributes of cotton.
This isn't to say that the screen-used was definitely not cotton, but in the pics above, it doesn't look like it. Like I said before. It would take some good hi-res shots to tell.