Could had been:
Different tire PSI,
Different IMA battery levels,
Different road circumstances (i.e., adjusting for other drivers),
Perhaps mileage indicator hadn't been reset when testing driving the others,
trove of other variables ...
Really, could be just about anything.
I feel my I2 broke in around 6-8k miles but really it could had been something as simple as the weather changing which does affect mileage, I cannot be 100% certain.
1989 Accord Coupe, 260k+ miles & going.
2011 Insight EX, 180k miles, RIP.
2012 Lexus CT200h, 80k+ miles & going.