I think what was mentioned in the first Episode of 'Picard' does not eliminate the possibility of the supernova being another star than the one Romulus circled around. Of course they say 'the Romulan Star' in the Interview but that can mean any star within the Romulan Empire. Yes, they said 'the Romulan Star' instead of 'a Romulan Star' but in the Interview they already mentioned the Supernova twice. So it is already clear which star they mean.
As creating a Black Hole near Romulus as a replacement for a sun makes no sense I still would prefer the variant with another star. (As a Supernova is just any 'star explosion' and we do not know all possible types of stars and their live cycles nothing speaks against some kind of warp fast 'subspace nova' - especially as we know that subspace energy can resemble a star as seen in VOY 'One small step'.)
But just implying it was Romulus' star that went nova makes sense for the new series. It simplifies the story as the event was 10 years ago the series is not about the details, not about Spock or Red Matter or Black Holes. These things are not essential for 'Picard' so no need top mention them.
As creating a Black Hole near Romulus as a replacement for a sun makes no sense I still would prefer the variant with another star. (As a Supernova is just any 'star explosion' and we do not know all possible types of stars and their live cycles nothing speaks against some kind of warp fast 'subspace nova' - especially as we know that subspace energy can resemble a star as seen in VOY 'One small step'.)
But just implying it was Romulus' star that went nova makes sense for the new series. It simplifies the story as the event was 10 years ago the series is not about the details, not about Spock or Red Matter or Black Holes. These things are not essential for 'Picard' so no need top mention them.