He might be referring to Shopify GMV (Gross Merchandise Volume —the value of commerce facilitated by the platform), which is probably approaching $100B per year.
No shopify market cap is $100bn; which is much higher than I expected. So I looked up their revenue, which is $1.6bn and they have an income deficit. so...
I think "100 billion business" means that the business (Shopify) is valued at $100 billion. (I'm not sure if that's true, that's just how I interpreted it)