@allyssandra
Is the ability to accurately pick a 10 rep max the same as not working hard enough in the gym?
I sort of agree with the point you're making - that just because they might not be able to guess the right weight for something they might not regularly do (only 10 reps), they're still putting in effort and working hard.
But on the other hand, the study also says that bench is their primary exercise, and they train it first, and often. So you'd kind of expect them to know roughly how much weight they can lift? And yet on average they overshot by 6, and over 25% of them overshot by 9 reps, which is, no matter how you slice it, a lot.
Like you say, it doesn't mean they aren't putting in work, but unless that work is close to failure, it's not going to mean nearly as much.
And on the positive side, it's not that hard to figure out how much you can lift. You can have fun (at least it's fun for me!) trying out different weights at different rep ranges, and going to failure. It only takes a few minutes to find your limit.