the CDC says 50th percentile is about 100 lbs.

https://www.quora.com/What-is-the-average-weight-of-a-13-yea...

http://www.cdc.gov/growthcharts/data/set1clinical/cj41c021.p...

93 kg puts them at something like 90th / 95th percentile.

So the mean height would have to be around 5'11 for them to just be "overweight" and not "obese". Which seems unlikely for a group of young teens.

Obesity in children is measured a bit differently. They use BMI-for-age percentiles, not Straight BMI.

From the CDC:

Overweight is defined as a BMI at or above the 85th percentile and below the 95th percentile for children and teens of the same age and sex. Obesity is defined as a BMI at or above the 95th percentile for children and teens of the same age and sex.

The study was on obese children. The paper says on day 0 they had a mean BMI of 35.6 ± 6.4.