True, it normally is the reverse: eastbound flights are faster because winds typically benefit those flights and slow down westbound flights. Schedules are designed to account for this. When the winds aloft change such that they don't provide a tailwind for eastbound flights, those flights end up being "late", even if they take no longer than westbound flights.

e.g. given on-time departures, a 4 hour-long LAX-ORD flight could easily be late, while an ORD-LAX flight that spends 4 hours in the air could be early. Why? Because the scheduled block times (gate departure to gate arrival) are lower for LAX-ORD.

Note that for short flights the time of day (i.e. congestion) often has almost as significant an effect on the schedule as the winds.

BTW: BOS-ORD is less than 900 miles.