If Muirchertach and Somairle were indeed allied at this point in time it may have meant that Guðrøðr faced a united front of opposition. If correct, it could also be possible that Þorfinnr participated in Somairle's insurrection as an agent of Muirchertach.
The potential alliance between Muirchertach and Somairle might have led to Guðrøðr facing a strong and united opposition. This scenario could also suggest that Þorfinnr played a role in Somairle's rebellion, acting as an agent of Muirchertach.