Hyperbole. She's nowhere near that. Not even close.
Today's celebrities are large fish in smaller ponds. Their fan bases are much more segmented. Sure, the biggest of today's celebrities still have tens of millions of fans, but in a world of roughly 4 Billion people, they are unknown or uncared about by an even larger pool of fans.
Back in the days of Elvis, the Beatles, and even Michael Jackson, media was much more focused through local TV and newspaper. The vast majority of the country (and even the world) saw a lot of the same things. Now, with such a myriad of different options, it's not uncommon for massively popular celebrities to go unknown to an even larger population of people.
In this case, the lionshare of her fan base is essentially the same as it was for Brittany Spears, KPOP, and all the 90's boy bands. Millions of young girls/women and male simps. Eventually her fan base will age out of their obsession and fandom just like they did with those that came before her.
Regardless, there are numerous other entertainers just as famous and popular. They just appeal to different, more mature audiences.