Many types of owls are cavity nesters but a fledgling is not going to move into a birdhouse. Birdhouses get used for nesting time only, laying and hatching eggs and raising the babies until they can fly away. That owl in the tree has already fledged and is no longer in the nesting phase of growth.
But some species will use "roosting boxes" at night or as shelter from a storm. A little birdhouse is not a roosting box.
But some species will use "roosting boxes" at night or as shelter from a storm. A little birdhouse is not a roosting box.