I didn't think YOU were mistaken but the ARTICLE you quoted clearly was. It referred to the Steiglitz MUSEUM as the Steiglitz MANSION. The clue for me was the address in the article. Having visited the museum, I knew it was located at Solyanoy pereulok, 13.
I value your contirbutions to the site, and only hope to clarify information that might confuse some readers. I hope you will do the same for me.