Earlier quoted context omitted.
Nazi and socialist ideology is quite close. After all, the S in NSDAP stands for Socialist, and they targeted same voters.
This is a gross misrepresentation and I hope that this belief isn't more widespread. The only thing that socialism and naziism had in common was the idea of an economy that will make a group of people better off, (which is pretty much the idea behind every economic model in history), but naziism is based on the idea of a "superior race", which is inherently better than the rest of the population and thus is entitled…
It's not actually believed, though. It's just an attack point to try and associate "liberals" with Hitler in Internet comments and what not. Pretty standard troll tactic.