Is Czar an official title in the US government? I thought it was just the name of the emperors of the Russian Empire which for some reason has become an informal pejorative term similar to tyrant?

It is an official title in the federal government.

Key difference from cabinet is czars aren’t subject to confirmation by the Senate.

It is an official title

No, that is the opposite of what the article says:

the informal term "czar" (or, less often, "tsar") is employed in media and popular usage to refer to high-level executive-branch officials

Thanks for clarifying