Opi - just my opinion, but I don't believe him. This is what happens to credibility when you lie constantly. Now he may not personally know him, but someone had to hire him and they vetted his routine before loading it into the teleprompter.

"I don't know him" or "I barely know him" has been a standby Trump line when he doesn't want to admit to an association with someone.

https://www.usatoday.com/story/news/politics/2019/11/23/impeachment-hearings-times-trump-said-he-didnt-know-acquaintances/4253186002/