My faux pas

I have a friend that is Jewish. Growing up here in redneck country I didn't meet any Jewish people till I got online. He is a great person that always remembers my holidays and I try to reciprocate. Recently I saw that it was Yom Hashoah and decided to wish him a happy Yom Hashoah on his Facebook page. Later, he writes to thank me but explains that wishing him a happy Yom Hashoah would be like wishing someone a happy 9/11. It turns out that Yom Hashoah is a day of remembrance of the holocaust. Boy did I feel stupid! No harm done since he's so nice and knew I had good intentions but I would have never done that. Next time I better look up the meanings of certain Jewish dates so I don't insult any of my Jewish friends.