Why would a commercial flight be landing with a tailwind?
Assuming 'I just' means today 17 Oct UTC time, then American Airlines 2539 arrived at 22:52 local, or 2:52 UTC.
Reported METAR at that time:
KBOS 170254Z 32013KT 10SM SCT060 08/01 A3015 RMK AO2 SLP209 T00780011 51027
The winds being 320/13 and runways 22L/R facing heading 215, that means the tailwind component was 3 knots. Well within the 737-800 limitation of 10 knots tailwind.
As for the why, it's to maintain the preferential runway system or to avoid switching back and forth if the anticipated winds will not shift more toward the other end. The preferred direction can be used in tailwind up to a limit (8 knots component in certain places for example).
For the US, acording to the National Safety and Operational Criteria for Runway Use Programs, it's 7 knots for the clear and dry runways.

Under ideal conditions aircraft takeoffs and landings should be conducted into the wind. However, other considerations such as delay and capacity problems, runway length, available approach aids, noise abatement, and other factors may require aircraft operations to be conducted on runways not directly aligned into the wind.
(...)
Where anemometers are installed near the touchdown zone of the candidate runway for landings, or near the departure end for takeoffs, any tailwind component must not be greater than 7 knots.

If there are no TDZ anemometers, then it's 5 knots.
The forecast agrees the winds will stay roughly the same and will shift more towards 220.
KBOS 162320Z 1700/1806 32010G20KT P6SM SCT150 BKN250
  FM170400 33009KT P6SM FEW250
  FM172000 21006KT P6SM SKC
  FM180400 23007KT P6SM SKC

Reading TAF guide: https://www.aviationweather.gov/static/help/taf-decode.php


According to the flight track, you landed on runway 27. And according to massport.com, below is the normal configuration for the NW winds. I should have checked the track first