True, but the "50% of the benefits of cycling" isn't accurate.
When I cycle for fun/exercise, with a heart rate monitor, I've burned (an estimated) as many as 650 calories in a half hour. A "normal" ride is typically closer to 800-1,000/hr. According to this chart[1] - a 150lb person cycling at a "moderate" pace would burn 563 calories.
In the study, people sitting in hot tubs for an hour burned about 150 calories per hour, which is about 2x what you'd expect to burn during an hour of sleep.
According to the study, sitting in a hot tub for an hour is more like 25% of the (calorie burning) benefit you'd expect from an hour of moderate cycling, and just under 20% of the benefit you'd expect from an hour of vigorous cycling.