... and there are three pitot tubes feeding three separate ASIs (the standby ASI uses the auxiliary pitot tube and alternate static port). You can have a democratic 2 to 1 vote.
"
IAS DISAGREE" alert should have been visible on the Speed tape with > 5 knot for 5 seconds Captain / FO difference above 45 knots, although that would be easy to miss, and 5 seconds is quite-a-ways down the strip.