Quoting wikipedia:
"During the period in which he won all six of his Hawaiian triathlons Dave Scott followed a strict vegetarian (vegan) diet."
Protein consumption as a growing child and teenager is directly proportional to height - it's the sole reason the average white male has increased 6" over the past 200 years. Genetics haven't changed, just our diet.
Holding every other factor (race, geography, culture etc) constant, the exponentially greater protein availability (in meat consuming countries) cannot NOT have consequences for general muscular build among the populaces and as a consequence, some form of athletic predisposition.
A good question to start with:
Are there any predominantly vegetarian regions - besides large tracts of India - elsewhere in the world?