If you can’t talk to him to find out his food requirements, don’t bring him food. From the diabetics that I’ve spoken to, there is no one single approach to eating. Low fat/low carb is popular, but there are still many diabetics that subscribe to the outdated sugar free way of eating. Low carb/high fat (Atkins) has a small following. There’s also diabetics that eat everything in sensible amounts. Some medicate their way through less sensible eating. Lastly, you have some diabetics that just don’t care and eat whatever they darn well please. As you can see there is no one single approach. For a person with food issues, a poorly chosen food gift can be disastrous. I wouldn’t risk it.
Bring a non food gift, make your peace, renew your friendship and learn about his approach to food. Once you know him well enough again, then you can buy him treats.