Of course anyone who was anyone knew. The US had broken the codes and delayed the Japanese ambassadors meeting to discuss a declaration of war between Japan and the US until after the attack. There is hardly a time this country has gone to war that the reasons were manufactured or misrepresented. Remember the Maine, The Lusitania, Pearl Harbor, 9/11, Egypt, Libya and Serbia. Of course don’t forget Vietnam.
Add to that the firing on Ft. Sumter was more than a probable event that was coaxed into happening (in no small part due to S. Carolina’s impatience), the Mexican War was a total scam, and the War of 1812’s main issue was resolved, but due to slow communication and way too many hot heads, no one waited for the news to get here from the UK.