There are lots of reasons for gas. But if you think you may have an overactive letdown (which often accompanies an oversupply of milk) then, yes, this may be the culprit. It is especially likely if you notice baby choking (or otherwise seeming to be overwhelmed by the milk flow) when your milk lets down.
Here's what could be happening: Your "foremilk" (the milk than comes first) is lower in fat and digests quickly. Your "hindmilk" (the milk at the end) is higher in fat and slows digestion. If you are producing lots and lots of milk, baby might drink more of the foremilk. The foremilk is digested quickly, dumping lots of lactose into his bowel all at once. The result? Yep, gas.
To help tame an oversupply of milk, experts commonly recommend limiting feedings to one breast at a time for a certain period. (For example, nurse baby on only your left breast from 8 a.m. to 12 p.m., and just on the right breast from 12 p.m. to 4 p.m., and so on.) This "block feeding" can signal your body to slow down milk production a tad. If one of your breasts becomes uncomfortably full during this experiment, express just enough milk to relieve the pressure.