Remember, for you non rails, there are many reasons to run slower than the maximum authorized passenger speed.

What was the signal indication?

Were they instructed by the dispatcher that there was conflicting traffic?

What is the gearing and maximum speed for that type of switcher?

Was there an actual "slow order", or other authority related reason restricting speed?

Was there any indication of wheel slip, or other mechanical problem with either unit?

Were they on overtime?

How close to a quit were they?

Was someone having intimate relations in the back of a parked car next to the tracks?

Is someone prone to walk around naked with the drapes open when the train goes by?

All kinds of reasons come to mind for slow running ..........