Yes they were right. You're only allowed pre-flight dining/supper if you're flying BA and only for the cabin you're flying in, ie a club passenger would have to take the Club supper, even if they had First lounge access (OW Emerald etc). I thought this was fairly well known, but realise not everyone does stateside trips.

You should haven't been in the First lounge, as you weren't on Oneworld, so it seems that some of the staff were going beyond the call of duty to keep you happy.

(I know some will take the view that there's no harm in trying, but I think it's a bit much to expect a F pre-flight dinner, when I wasn't travelling with BA).