Unfortunately this is indeed policy at BOS...several of us have ranted about this on other threads in the past...

EDIT: after reading the post from itsmeitisss further down I realise that his post is a truer picture of the situation...Whilst I could use the F lounge I was not allowed to eat in the F dining room for sleeper services...however, some locations have made an exception and allowed me to eat from the CW buffet on such occasions such as at ORD.

Sorry to hear you weren't aware of this before heading there. Hope you have a good flight back anyway.