I apologise for yet another 261 question - I have explored the Wiki, it's a hive of information but I can't see a specific reference to my claim, your advise please:

Last June my wife and I were on a 2-4-1 LHR/BOS in F.
Evening flight. After a couple of hours delayed on the ground, even the meal was served while waiting, we were de-planed at midnight. "Operational issues" we were told and BOS was now closed.
We spent that night in the Sofitel and we flew the next evening. BA settled our hotel and some small toiletries. We kept the claim to the minimum as we ate in the lounge.
I submitted a claim and may have missed the 261 part, and many weeks later the hotel and toiletries were settled in full. Thinking I may have omitted the 261 element I resubmitted with explanation.
This morning I received this rejection:

'Your claim's been refused because BA0239 on 29 June was delayed due to London Heathrow resourcing issues and subsequent problems with Boston not allowing the flight to arrive after 04:30 GMT.'

Is this a legitimate get out?