It's most likely a default value.At least that's how it reads on our MD-80/90 readouts when a powerchange has occurred and no pilot-selected value has been entered.
You may well set 100 kts in the readout window during flight,however,the Flight Management System will prevent the plane from decellerating below Alpha (min speed for present configuration) and the Flight Management Annunciator will show ALFA SPD and control speed to applicable value.
But things can (will) go wrong,and no pilot in their right mind would set such a low speed in the readout.
Although it is probably not the case here, as evidenced by the well informed posts above, there is always the possibility that one of the segments on the speed display is burnt out. In other words, maybe 180 is set but 100 is displayed because the center segment of the "8" is missing.
Not quite related, but after landing, we always set the parking bay number as a reminder in the altitude window, so if bay 1 we set 100. Bay 10 we set 1000. It not a company requirement and it not written anywhere, but more something that we just do! just a reminder as sometimes the taxying can be complicated at some airports so you don't want to forget the bay number!
Well take a look. The PFD display is almost displayed in black, meaning that they have just turned on the APU system. Like on the MD-11, when everything is first set up, the autopilot console will automatically will show a reading of the standard IAS as 250 knots. Or it could just be in a test mode. But again on the MD-11, it will say as "Fail" on the PFD.