They run on the sideline of the football field, first and foremost. Pretty sure Indy doesn't have a 1-off piece of astroturf that is so unique that it would be inappropriate to time a player on another field. Secondly, why would the NFL have a different clocking system for this event? If the field and clock were both different, what's the point? It's not like this was a workout, it was a regional combine.
If you want to say that his 4.19 won't be recognized as official because it was hand time and the official times come from the electronic timer that's fine, I guess. Kind of begs the question why teams have personnel hand time players in addition to the electronic timer.
Different track and different timer.....somehow the Olympics make it work, but the standard for the NFL must be a little higher than that.