Liberalism historically from its inception has believed people have certain rights, right to “free market “ as they say is one of those. In the US Democrats also go by liberal, but not all liberals and democrats know their position is definitionally pro capitalism and liberal has taken on a definition of left of conservatives/republicans that most Americans have not dug in that far.

TLDR To speak American politics their are conservatives/Republicans and everyone else is liberal, including in that camp progressives, leftists, Bernie Bros, anarchists. To speak Leftist politics, you have Leftists, Anarchists, Liberals (including conservatives, liberals, progressives because all their policies are pro capitalism )

Democrats are a political party, one that hasn't had a consistent ideological set of beliefs throughout its own existence. For that matter neither has the republican party.

They are not "by definition" pro capitalism.