There is some truth to this. To get the most from BJJ you need to be in somewhat decent shape from the beginning. It helps not to be super fat so you won't have mobility issue or be chubby with really bad cardio.
I had really, really bad grappling cardio for first the 3,4 years when I started training Jiu Jitsu. I mean I could literally only roll twice before I ran out of energy, became out of breath, be exhausted, and get cramps here and there. I believe no other students had the same issue as me. I felt like an outlier.
Some people do need to get in shape on their own, first, before BJJ can benefit them. In my situation, no amount of rolling would have helped my cardio because I was just getting worked on over and over again, and not doing much of anything to combat that.
I was able to improve my cardio and be in better shape(even though I'm still out of shape) by regularly working out on my own outside Jiu Jitsu class. Now I am getting more out of BJJ simply because my body is now better prepared to handle training.
I think normal skinny people or people with normal/average cardio and strength abilities take their abilities for granted because they don't have very poor cardio/stamina/endurance issue to begin with. So its much easier for them to start training BJJ from the beginning with no issues.