This was pretty much a common opinion among the scientists of the time.

Stars were definitely known to be very very distant, and this had been known for a long time because of the inability to detect any parallax in the stars. This meant that the distance to the stars was huge compared to the distance of the solar system planets.

Also, it was a common idea that other stars had their own planets. And that none of these stars/planets can properly be said to be in the centre of the universe. After all, if the universe is infinite in extension (which they believed it to be), there is no centre.