[General] The answer to "You are more than welcome to ..."

[reza_p_o]

The other day, we were a group of people going for lunch and saw an elder professor. One of us insisted him to come and I told him: "You are more than welcome to join if you would like so." He responded: " Of course I am. But no!"
I was wondering if this is a common answer to my sentence and if he got offended and answered that way?! Was it something like, "You kids don't get to tell me if I am welcome or not!"??

Thanks!

 

[MikeNewYork]

Not common. He was probably just trying to be humorous. That invitation could not really irritate or offend anyone.

 

[Raymott]

I think he meant "Of course I am interested. But no (I can't at the moment)". I know you didn't say "...if you're interested". Your question isn't grammatical, so that might have thrown him off answering correctly too. This happens in conversations.
Naturally, his tone and body language would count for something.