That is exactly what I want to see down here this time of year. Any yes, it is bearding. Have you checked the hive to make sure they have plenty of room? As long as they have room, then you can say "Yah Hoo!". The more amazing this about those bees is they won't even wait for sun up to start their day. They will be gone as soon as the sky shows signs of beginning to lighten. Bottom line...that's perfect. Just make sure they don't need another box. Our flow down here is still kickin'. I see you have a double brood box. I run single deeps or double mediums for brood. You can likely split this hive with NO problem, maybe even two splits. Thought about it??
Edited to add, make sure your inner cover has the groove up and to the back, then push the outer cover back. As an additional note, I started with all solid boards, then jumped on the "SBB" bandwagon. Bottom line, I am converting all back to solid bottoms. They have outperformed the SBB's in every case, and ventilation has never been an issue. Just don't go too high on your boxes. We don't need to build booming brood boxes like the folks that have to over-winter do.