But, even then, SciAM "writers" knew better than to infllate "a dozen" into "Tens of Thousands"... :-{
When you read the article (you did, right?), it said that ‘singleton’ binary black holes are the ones with accretion discs and thus detectable. The ratio of singleton to undetectable isn’t known, but it doesn’t seem unreasonable for there to be a hell of a lot more undetectable black holes that aren’t presently ‘feeding.’ Tens of thousands? I don’t know. Perhaps you have a more accurate number.