No its not. The sun and moon 'appear' to be the same size thats all.   Its all a matter of perspective.   Here's a simple demonstration. Here I have a small plate, and an upright fan. In this photo, from this distance, the plate looks the same size as the fan.   But in reality, it isn't. The plate is actually much smaller than the fan, as you can see when I put them next to each other.