That's a bit of a stretch. They don't seem to publish much info, but they do publish quarterly shipments. According to macrumors it's more in the range of single digit millions a quarter for their all computers, 4-7 usually.

Maybe, just maybe, they are reaching that billion this decade or so, but looking at those numbers it's rather in the range of 10% of that.

Still a huge number, but that's a fraction of PC market.