It is possible his 1% body fat was an estimate or used a different technique to measure. I know nothing about it really, but it is possible he was more interested in training than finding a doctor to give him exact stats.
Saying "1% bodyfat" doesn't really mean much, because even the most accurate methods of measuring bodyfat have a not insignificant margin of error. And skin-fold calipers, the most common way (in my experience) of measuring bodyfat, definitely have a significant margin of error.
You might actually read 1% on the skinfold caliper, but that doesn't necessarily mean you literally have only 1% bodyfat.
