Tankie's original use was for British communists who supported Soviet military expansion. In the modern sense, it is used to describe communists who are authoritarian-apologists. For example, a communist who romanticizes the Soviet Union or makes excuses for the Uyghur genocide is a tankie. I've also seen it stretched to include militant anti-capitalists, or more commonly, "militant," anti-capitalists who call for violent resistance to capitalism from the safety of a keyboard.
Democratic-Socialists are not tankies. Socialists are not tankies. I don't even think most communists qualify as tankies. Criticizing Democrats does not make you a tankie. Condemning Israel's human rights violations does not make you a tankie. Voting third party doesn't make you a tankie. I see this term used here every day, but never correctly.
"erroneously a socialist" oh come on. All communists are socialist but not all socialist are communist. You can't just change definitions of words because you are a left-anticommunist. I don't even know what to say besides read a book.
Did you read the self identify part?