To me the phrase 'receiving upside's means he's going to have more catches, more receiving yards, and more receiving touchdowns than a running back who barely catches the ball
As you can see it's more than just catches that matter. Also running backs usually have a much higher yards per catch than they do yards per rush. Another reason catches are more valuable.
A good back's 5 yard rush is worth .5 fantasy points.
A good back's 8 yard catch is worth 1.8 fantasy points.
Catches are typically worth more than triple the fantasy points in PPR
Derrick Henry is coming off of a 2,000+ yard season. That's a huge season and will likely stand as the best season of his career. Why? Let's take a look at every other previous 2,000 yards rusher and what the season after their 2,000 yard season looked like.
1973 O.J. Simpson. 2,003 Yards. - in 14 games.
1974 O.J. Simpson. 1,125 Yards.
Not much changed for Simpson from one year to the next, he wasn't as efficient and didn't get as many carries. The few years after he did well again though.