Scareactors are not allowed to leave the houses until the last guest is confirmed to have gone through. Looks like you, unfortunately, went through at the time of a cast change.
This is always a possibility. I've been through completely empty houses early in the night thanks solely to bad timing. However, having known a number of scareactors, I can also confirm that during unplanned event extensions there have occasionally been times where leaving before the guests did was presented as an option, and many took advantage of it.