You had less than 70mph average speed. The car computer said 52mile and 48 minutes. This means 65mph average speed. So it would have worse mpg at 70mph real avg speed. So it would be correct to mention the actual average speed at the end of the test.
The average speed he mentions is the highway only. Actual average speed is a flawed stat because you can drive 200miles at 70 but if you’re stuck in traffic for 15 mins it’ll skew the stat.