The 5096 was an official public measurement that was performed and recorded at the Combine in front of media people, cameras, and representatives from all 32 teams. It was also later confirmed at his pro day under the same public circumstances. If those measurements had been off by as much as 1", not to mention 2", it's hard to believe that none of the numerous independent observers of the measurement process would have noticed and spoken up.
He might be 5'9"....but with a helmet and cleats...that clears 3" at least (shrugs).
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My thought:
The Patriots secondary needs to KNOCK Tyree Hill and Kelce on their butts whenever Mahomes leaves the pocket. It is legal to do so. See link: Why Richard Sherman’s leveling of a Bills receiver was legal