I believe that Mikesch was a brave boy yesterday :) I had the same experience with Donna, Willi and Moritz. The first day it took them hours to go out the first time and they came running back right away BUT the third day already it was difficult to get them inside again, so....... :)
Good news. Maybe he remembers how bad it was outside for him. Hopefully he knows your house is where he gets his food now so if he were to get outside the yard he would come home for food.
After all my anxiety, it ended up for nothing. It took him 2 hours to cross the threshold with the door wide open, and then when something spooked hi, he ran right back into the house. He's spent 7 months of his 9 months (estimated) in the house, so this is definitely his home!