Robbie is frustrated with his unlimited cellular plan because he's being throttled relentlessly. So bad to the point that he can't really do anything. But when he signs onto wifi, it's just fine. So they signed up for a 10GB plan, it was much faster. Leo says that unlimited doesn't mean "as fast." And on Verizon, some of the plans will throttle from bite zero, some after 5GB. There are five plans in total. So you have to read the fine print. It sounds like Robbie had the Unlimited "start" plan.
All cell companies that offer unlimited have gotten in trouble with the FCC for playing fast and loose with the rules of "unlimited" and what it can really mean.