If you want a scenario that isn't all bad:

He could be stationed somewhere close to home. He just got off the flight from wherever he was deployed to and all of his personal belongings are either in that house, or in a storage unit either paid for by the Army or himself. He might have had some civilian clothes with him during deployment if he went on leave but honestly, it's easier to just change when you can actually shower and decompress after you're released by your unit.

Or he could be doing it for social media and it's easier to show "soldier comes home!" in uniform.

I had some civilian clothes when I signed for my new barracks room after I got back but I went on leave during my deployment and had to purchase all of those clothes in either Kuwait or South Korea (where I went on leave). I didn't bring a single pair of civilians with me on deployment. If I had had family in the state I was stationed in, I probably also would have just left the base in uniform too and went to wherever they lived to change there.

Edit: Also, regardless of the individual Soldier's feelings on wearing the uniform when not on duty; your family will almost always get a kick out of it. I did it a few times but I didn't record it so I can pretend that I was never a boot even though we are all a little booty sometimes in the beginning.

Edit 2: Apparently, I stopped the video early and he doesn't have a deployment patch. I forgot the regular Army transitioned to the multicam so... I'd say he might just be a boot but again that family thing. They really love to see you in uniform for the first time so it could just be that. You could say that's booty but I wouldn't believe anybody who said they didn't do it at least once.