Cummings says that he warned Boris the drinks party was against the covid rules.
Boris says he didn’t. www.bbc.co.uk/news/uk-politics-60039868
So, given the track record, AIBU to assume that BJ is either
(A) lying to Parliament, or
(B) so bad at his job that he has no idea what his private secretary is up to, or what the rules he created actually said, or what the difference is between working and having a drinks party.