Suggestion for future discussions with your dad. Ask questions. Get your dad to explain himself. Questions can be less threatening. And keep a sense of humor.
E.g. something like this:
"How can it be that JWs believe in creation but they deny they are creationists?"
"Ah creationists believe God created everything in 6 24-hour days and JWs don't believe that."
"But you're describing Young Earth creationists. Are you aware other types of creationists exist? Can't JWs be classified as Old Earth creationists?"
"No. JWs are not creationists."
"I don't understand. The dictionary and encyclopedia definitions say creationism means [blah, blah]. JW beliefs fall within that description, don't they?"
"The dictionaries and encyclopedias have it wrong."
"ROFL! Really? What do you think the proper definition should be?"
[Allow response.]
"LOL. Maybe you should write in and correct them, dad. You're a hoot. Hey, let's meet up for lunch."