Labour are (somewhat successfully) being sold as the opposite of the Tories, due in no small part to Facebook memes and "MSM is anti-Labour" posts on social media. People are being lazy and taking that as "We're against Brexit, too", when the reality is very different.
Mini-rant:
A lot of what Labour supporters are doing is actually pushing England towards a two-party system. In every single Facebook or Twitter post I've seen, Labour policies are contrasted against the Conservatives, not the LibDems or Greens, who are closer to Labour in all ways. They're differentiating Labour solely against the Tories, and what that does is create the perception that there is only one party that can stand against the current government.
It's actually pretty interesting looking at how bad Corbyn and the Labour Party's public relations are, to then look at all the pro-Labour almost-propaganda techniques being used by the grassroots/social media/non-MSM Labour supporters.