If I had to guess I would guess they meant against Twitter. IMHO the EFF should be biased against Twitter given their mission, so I wouldn't even consider it to be bias personally.

There should be a social norm where if you're going to call out a bias, you should name the bias (at a minimum) and share the bias you see that bias from so readers can calibrate their interpretation. Without it, we're in a situation like this where someone has to ask and others try to work it out and a lot of time is spent trying to understand the claim rather than have a discussion.