This happens all the time with trans atlantic flights. The Boston controllers in this case are separating just for basic radar, they may try to set up Moncton with some sort of help for the non-radar separation that will be required but their setup may not fit into the the full scheme of things down the line. Transitioning from radar separation to non-radar means going from 5 miles to 10 minutes of separation at altitude. So the Boston controllers likely climbed the Air France flight, then Moncton got them, went to coordinate them into non-radar, found out their altitude was not going to work, and had to descend them for traffic. This happens every night for a lot of planes going out over the ocean. Not everyone can get their altitudes and they need to descend or climb to an altitude that may not be optimal for fuel consumption.
Many of times pilots complain about it, delay their descents and start asking questions as if "XXXX descend and maintain FL330" is not an ATC clearance. It is, do it, then ask questions. They can get all pissy about it but we controllers don't make the rules we just separate traffic using them, and he was apparently a little late to the show and missed out on getting his altitude. Typically as the bunch that is using up the higher altitude goes across they will all ask for higher and by the end of the flight everyone will gain 3-4,000ft on the way across.
