They processed $50B is perhaps better way to put it, 50 B is not their actual revenue yes.
However using GMV[1] as a proxy for revenue is fairly common practice in retail industry. Walmart's revenue in similar sense is not really $500B, while it bit more complicated as Walmart buys from producer/ wholesaler and sells to the consumer (less so by Amazon as significant chunk of their inventory is owned by the sellers directly however revenue numbers are counted the same way).
The revenue for their operations is only the difference between selling price and buying price, profit is after you remove the cost of operations from that number. Ecommerce / travel/ delivery startups etc have for long time used this as somewhat misleading metric.
This practice used to particularly annoy me few years back, during fundraise pre-series A especially angels used to somewhat blindly compare retail statups "revenue" with SaaS startup numbers.
> and generated about $15 billion in revenue for Apple
the 50 B is total gross sales.