There's nothing disrespectful if Bitcoin is considered as a gambling device. As long as it is legal in your area. And as long as you play responsibly.
In my opinion, using Bitcoin for gambling is positive because its shows that Bitcoin is recognized as a trustworthy and legal way of payment.
Do you really don't see that reducing independent money to a gambling device is disrespectful? He's trying to belittle it and make it look less important and less real than it really is. He can see a growing economy that is beyond his comprehension and it makes him angry. Maybe he thinks that bitcoin is attacking the current world order and he made money there so he stands to protect it?