It's not. However, I experienced this same anomaly in Waco testing. I had 2 or 3 speed tests that exceeded the maximum speed. Up to 40Mbps. However, when I would do speed tests immediately after the 40Mbps result, they would always drop back down to 37.0-37.5 Mbps speeds for the next 10-12 tests. I just chalked the results higher than 37.5Mbps as inaccurate anomalies.
Not that there is any noticeable difference between 37.5Mbps and 40Mbps.
Robert via Nexus 7 using Forum Runner