رَجَعَ خَالِدٌ وَهُوَ مَسْرُورٌ إِلَى بَيْتِهِ.
Khalid returned home while happy.
'Wa-huwa masrūr' gives the state accompanying Khalid's return and therefore functions as a circumstantial clause. Contrast:
رَجَعَ خَالِدٌ ـ رَحِمَهُ اللَّهُ ـ إِلَى بَيْتِهِ.
Khalid—may God have mercy on him—returned home.
The prayer does not specify the manner or circumstances of returning; it interrupts the main utterance to add an independent benefit. That is parenthesis (iʿtirāḍ). Their similar placement does not make their rhetorical function identical.