This scene really highlights Alastor’s insistence on being an observer of feeling as opposed to someone experiencing it, deliberately placing himself outside of the group of “wayward souls” physically and emotionally. His phrasing throughout makes their connection sound like a story he is narrating from the outside, that it could never be something he has become part of through his time at the hotel.
“It almost makes ONE sentimental” is even further distancing — that the emotion and care shown between the hotel staff before the extermination has the ability to affect, but not Alastor. Never Alastor. He has rarely, if ever, stated emotions from an “I feel” perspective, instead constantly filtering it through commentary as opposed to experience.
This language of detached observation is a constant attempt to pretend he is just enjoying a show rather than becoming an integral part of it, that unless he is able to script his own action, benevolence, or care — he will remove himself from the narrative.