A kilobyte of text is roughly half a page of text. If the 45TB does not include the size of metadata, then that comes out to roughly 3,000 pages of text per living person on the planet. Especially when you consider how little of the world's population is online, and how much writing isn't preserved, that would probably be a double-digit percentage of the total extant digital written record of humans.
(This makes me think that the size does include metadata size or markup. But even if it includes those things, you're still probably looking at 0.1-10% of the extant digital written record. The only way it's not a significant fraction of all extant human writing is if the size is also including copious amounts of non-text data, such as embedded images or videos.)