Do they seiously believe that doing better in the local elections last night means that
a) most people that switched to them agree with their national policy to remain in the EU and/or,
b) they will suddenly be a major force in the next General Election.
Instead the reality is that Labour and Tories are currently not worth voting for due to many issues including the Brexit debacle.
So as the vote was only about who runs the local council (hence the low turnouts) it didn't matter who people voted for as long as was not the Conservatives or Labour.
If a General Election happens the Greens and Lib Dems will still have a minimal amount of MPs. Especially when the Lib Dems have still not been forgiven for abetting the Conservatives for a little taste of power.