Glad to see your betta is doing betta! I had two bettas who both got velvet at the same time and a coworker's betta who also got it (they come to me when their fish get sick, LOL). Here's how I knew for sure what it was and how I cured it.
Turn the lights off or go in a darker room with your fish bowl and shine a flash light on him, if he looks like he's been sprinkled with gold fairy dust, then it's velvet.
To treat I used a product called Quick Cure and raised the temperature in the bowl to about 85 (I used a heating pad set on low to achieve this, note, if you attempt this you will have to monitor the water temp constantly, it's risky and you don't want him to boil), couple days later, it's gone. Change water, do half a treatment, just to make sure, wait three days, fresh water.