If the visualization by VASAviation at
https://www.youtube.com/watch?v=cXNWwKx9c1o is anything to go by, it looks like the situation started when the previous aircraft, SWA3117, exited via TANGO instead of DELTA. Since UAL2065 was already on TANGO, holding short of the also active 28L, I guess the controller was concerned that the tail of SWA3117 would be too close to 28R. When AC781 failed to acknowledge the go-around, the controller solved the problem by a) asking UAL2065 to - without delay - cross 28L despite company on 2 mile final and b) asking SWA3117 to pull all the way up to the 28L hold line. Both instructions in a rather hurried voice... So, some quick thinking by ATC meant that the runway was clear when AC781 touched down.