Those numbers are pretty close to actual floor space required for the sofa. In other words, outside dimensions.
The seating area on mine is a little deeper than many household sofas, I'm talking butt and upper leg room. I am 6 feet tall and I can lie down "inside" the sofa but my heels will be up on arm at that end. My wife at 5 feet 6 inches can lie down inside easily, even use her pillow. She does that while watching TV and I recline in the driver chair rotated toward the TV. We got a nice foot stool at Wally World that has a hinged top where we store the vacuum that cleans the floor.
I only opened the sofa out one time, just to see how it worked, and I don't remember the bed size. I do remember it was larger than I thought it would be. A small couple or kids could sleep there nicely.
And, YES, the sofa would seat three adults with no problem. 4 if they were friendly.
2015 Jayco Precept 35UN
Towing JEEP TJ with Roadmaster plates and bar w/Blue Ox Patriot brake
an Aluma low bed trailer with HD Road King and/or Polaris RZR onboard