How Strava calculates your maximum speed on activities:
Strava calculates your max speed in a such a way that any GPS error can cause the value to be greater than expected. To calculate max speed, Strava looks for the fastest speed recorded between any two GPS coordinates recorded in your activity.
If for example your GPS is not recording accurately, and one GPS coordinate is recorded + or - 50ft from where you actually are. Then, the next GPS coordinate is also recorded + or - 50ft from where you actually are in the other direction. Between the two points, over the set time interval, Strava will think you are moving faster than you really are because the distance between the two GPS coordinates isn't accurate. The good news is that these high speeds generally occur for the span of only one GPS point, so they don't have an effect on your activity's average speed or other statistics.
To complicate matters more, on the Analysis graph there is a little bit of smoothing because we do not plot every data point but instead every 3 or so to make a readable graph. If you look at the analysis graph, you usually won't find the same max speed as is reported in the activity stats because the graph is smoothed.