Glycemic index level would be the same. However if you're eating the white rice the moment it's finished cooking it is not a resistant starch it is a quick carbohydrate. The glycemic load will actually be pretty high. However the watermelon I'm eating has an extremely low glycemic load. As a matter of fact it is a two out of a scale of 100. Not much can be eaten that lower than that.
What does that mean? You and I could eat the same amount of calories you with your rice me with my watermelon and I will most likely eat a lot more watermelon then you would your rice however due to the low glycemic load not only will I'll be fine other than maybe having to visit the restroom do the water content but I could eat a large bowl and not risk impacting my blood sugars in a negative way or even gaining weight. However you risk impacting your blood sugar as well as gaining weight. Now if you were to take that same white rice and put it in the refrigerator overnight to cool, you would then have impacted that rice into becoming a more resistant starch. And then eating the same amount even if you were to reheat it would not have as devastating and impact on your blood sugar as well as your risk of increasing weight although the impact would still be exponentially higher then we eating that watermelon.