That is the average speed over the segment.  On flat, paved roads with a tailwind or riding in a pack (maybe a race), that speed seems achievable by stronger riders.  It is only about 32mph.  Most strong riders can push up to and beyond that kind of speed in a sprint on flat ground.  It could also be a case where someone left their GPS on in the car on the drive home after a ride.  You would have to look at the specific activity to see for sure. If that was the case, you can just flag it to remove it from the leaderboards.  Flagging can only be done from the web version of Strava and not from the app.

Thanks for the reply. Useful to know it is average speed...though that makes it all the more impressive. 

we do have some pretty intense winds up here...so no doubt thats a big factor on a lot of the coastal KOMs. I think what I lack in strength as a rider, I make up for in suspicion and jealousy!...so no doubt I just need to work harder (and maybe choose my wind direction days better).