P.H.
He is just pretty excited to be free of the crib, so let him get use to this new way of sleeping for a little bit. He still needs his naps and you are lucky to have him napping this long (my son went until after 4, but this is not as common as we would wish for little ones)
Maybe start haivng a story time and a quiet time around his schedueld nap time and ease him into resting. This extra freedon of being able to get out of bed is normal and since he is older it will be a little while before you can get him not to just get up and wander around.