According to Wikipedia it’s weight:
US regulation FMVSS 208 requires that bags be engineered and calibrated to be able to "save" the life of an unbelted 50th-percentile size and weight "male" dummy.
Assuming the regulation in the EU is similar and given that US average weight/BMI is higher than European average US airbags need to be bigger.
A super precise and methodical dumbass makes a very good data/sample collector IMO. I’m glad it worked out well for your acquaintance.
Also I think nearly anybody can provide value / is valuable to society. If all of us were super geniuses society would collapse.