Yes, Ryumin has his own priorities. The work was done on a short notice and he was just being professional.
But there are still ways to prevent Yooil from wasting her time waiting. He should have at least informed her before going to the recording. Or maybe, he should have just taken his phone to the toilet and texted her while doing his business there. The point here is, there are ways to avoid this pitiful event.
He can pay her money back. But nothing can ever be exchanged with the precious time she spent there being excited and worried about him.