I doubt the guy personally knew anything, as far as facts, regarding the Steele dossier, but out of his preexisting animus toward Trump, he “vouched” for Steele’s work, without knowing the veracity of it at all. Then the U.K. was stupid enough to make the guy Ambassador to the U.S.
If anything is disturbing the U.S.-U.K. special relationship, it has, for at least three years, been the U.K. government, and its political collusion with a U.S. political agenda against Trump.
He is vouching for Steele and has not stepped back from that original statement so it appears that he is endorsing the veracity of the Steele document.
I doubt that he didn’t know that it was manufactured to hurt POTUS.