Here in the states IFR aircraft can be placed at or even request the "wrong" altitude for direction of flight, depending on preferred ATC traffic flow, weather (icing or storm cells), or unfavorable headwinds. This happens all the time, but of course the caveat is that ATC first ensures that this altitude does not conflict with nearby IFR aircraft in the other direction.
One prime example of this is filing IFR to the west out of White Plains, NY. If an IFR aircraft files for any altitude below 10,000 feet to the west, that aircraft will be given 9,000 feet (the wrong altitude). This is done to get these departures above the Newark arrival/departure corridor.
I am not familiar with Canadian airspace regulations so I cannot say if the controller in this case were enforcing a regulation or simply concerned about a traffic conflict further down the route, but most likely the United was placed there by ATC farther back. Personally I do not see a reason for a NASA report.