Its not at all logical, but Vegans originated on the planet Vulcan.
I hesitate to correct your factoid, but it was 'survive on one lentil for 40 days' hence the lack of vegans at that time..The religious ritual of a time of fast and abstinence was originally a period where meat, fish and dairy could not be consumed, and adherents had to follow a vegan diet. Some extremists took this further, surviving for 40 days on only lentils.
This is where the term "Lent" comes from - a period where only lentils were consumed.
The word "flatulent" comes from the same source.
True that /\/\/\
I gave up cooking Chinese food because my wife kept kicking me in the Harry Rollocks and calling me names, having read about this and being rather dim.