Thinking about this more, I think Thomson didn't bring in Hoffman to start the ninth because he didn't want Rosario, who would sure have pinch-hit for Pillar in that situation, to face a RHP, quite possibly with runners on base.
Of course, it was also playing with fire a bit to leave Soto in. Soto has had command issues all year and was not throwing a lot of strikes to Olson in the 8th. It seemed almost inevitable that he would walk someone and bring the tying run to the plate. I guess in that case he would have brought Strahm in to face Pillar.
In retrospect, there were risks no matter how Rob played it. We have to say now that he made no decisions in this game that resulted in a bad outcome.