Because some foals are born with darker colored eyes. I've had some that were brown/hazel and some that were the blue shade same as what is shown on this foal in your photos. As they darken they look less blue; some may turn burn as said earlier, others I believe do stay blue but they are such a dark blue you have to look really close at them to see that they aren't brown.
If you have the true crystal blue eyes associated with splash or frame they are obviously much lighter, and they may even lighten up more as the foal gets a little older. People used to call them wall eyes, and many people didn't want them because they were considered "wild" and undesirable. In some breeds, like Morgans, the blue eyes were not allowed--blue eyes automatically excluded the foal from the registry. A foal with eyes the color of your foal's eyes were not discriminated against--because those eyes turn dark and are not an indication of any pinto gene. (Morgans are now allowed to be registered even if they have high white and/or "blue" eyes.)