Insulin. I forgot to mention that in the previous post.
The carbs are providing you with an insulin spike, which increases blood flow. This is why you notice a bigger, better pump, but carbs will not further increase your body's creatine storage capacity. You creatine stores will be maxed out in about 30 days with 3-5 grams daily. At that point, adding more carbs will not further boost creatine storage.
What you're experiencing are independent effects from both the creatine and the carbs. You really don't need a giant insulin spike in order to max out your creatine stores. The creatine is going to di it's job regardless of whether you take carbs during training. Those older school supp companies used marketing to fool people into thinking that the customer NEEDED massive insulin spikes in order for creatine to provide optimal effects. It was and remains untrue to this day. But, when these companies add 75 grams of dextrose to creatine (old cell-tech) and then the customer notices additional weight gain and better pumps (along with a diabetic future), they think the supp company was telling them the truth. In reality, the customer spent $60 for $1 worth of sugar and $5 worth of creatine mono. Cell-Tech made a freakin' killing selling creatine mono and sugar for $60 a jug. Hey, I also bought it 26 years ago when I was 20 years old, so no judgment here.

Even with their massive advertising budget (which is what people were really paying for), they still made a killing. Maybe a "raping" would be more accurate.