Why do so many ancient societies claim their god came from the star we now call Sirius B?

I would just attribute that to coincidence or even ancient people communicating across the globe via ships, if the star were visible to the naked eye, or even simple telescopes. How did they know of this stars existence, and why is it special? And why is it always the same story, with the god always having an long skull, having an odd shaped body, and taking over the native beliefs then destroying mention of other gods and demanding to be worshipped?