This doesn't equal out to 2.5 billion people a day. One requests does not equal a unique visitor. For most cases that doesn't even equal one page load. I don't know where the 29k/s number came from but I guess its a peak load from one of these bench marks. It isn't realistic to expect a server to be consistently pegged at 100% 24 hrs a day. The real number is going to be a tiny fraction of that
Sure, as long as your website is just a tiny piece of plain text, and all your requests are distributed perfectly evenly over the course of the day, and every person only requests a single file and then leaves. But since none of that is even remotely close to realistic, your numbers are not either. Yes, 29k req/s is quite slow for a "serve a tiny static file" benchmark. No, you can not handle a billion visitors a day on one server with such low performance.
That's far more capacity than anyone needs and if your site does ever reach the point where 2.5 billion people visit it per day then you can just put another box up and double your capacity to 5 billion requests per day.