Because the 3.5 km marker is just outside the entrance to Temptation and the 8.5 Km marker is outside GOV (hence 5 km or 3.1 miles). Also the address for GOV is Blvd. Kukulkan KM 8.5 and Temptation is Blvd. Kukulkan KM 3.5.
Impressive and educational I thought maybe you snuck a peak at bus's odometer that day we all went over.