A was helping himself. Or, A was helping the boss; A might have sensed that the boss had some uneasiness with this assignment. In any case, helping you was not the issue.
A certainly took some glory away from you. You were eager to distinguish yourself. Should be more aware what was motivating yourself.
Should have discussed your questions further with A, in light of A's long text, before posting them to the vendor, who is an outsider.
(When you feel irritated, was that an outcome desired by someone?)
