Like everything, it really depends. It is pretty easy to pop babies because their bones are still relatively pliable, and they don't posses the strength to hold their hemipenes. If done correctly, popping babies poses little to no danger. Same with probing. If you don't know what you're doing, it's easy to ram the probe in too far and hurt the baby. But if you do know, then it's safe.
However, for some snakes that are born very small (GTPs, ATBs) and delicate, popping is safer than probing.
It depends on the snake, and the person, but the quote is not incorrect.