Ha ha that's adorable! Yes that's a play bark! My Nellie does it all the time. Sometimes when she's in her crate by herself she will roll around and bark like that. Or she will run underneath the couches and bark at nothing lol. Rico has luigi to play with!
Awwwww! It took Bambi 2/3 weeks to bark after we got her. We were so surprised but knew then that she was settling in. Wait until he gets frisky and makes some really funny noises. First time my husband and I heard Bambi play with Ginger, we thought she was sick or something. Some of their noises will melt your heart.