Test the tank for water quality thoroughly...temperature, ammonia, nitrite, nitrate, pH, SG
, calcium and alkalinity to start with. If you suppliment iodine, strontium or iron, test those levels too. A wandering anemone is not a happy one. It is normal for anemones to wander a bit after introduction, but there does come a point where it can indicate something with water quality (sometimes lighting) is making it unhappy.
Hard to say if the fish you lost was due to the anemone's stress, coming into contact with it's tentacles, or perhaps died of something else that maybe the anemone is showing a disliking to as well. Haitians are a bit more aggressive than other commonly kept anemones. They are more quick to sting. An anemone on the defense will have it's tentacles stiff and stout instead of relaxed and flowy. At least if it foots, it's aggressions are limited to how far its tentacles can reach, but one on the move can bump into things.
We, as a people, know so much more about outer space than we do about our own oceans. This lack of knowledge can very well spell the dangers that lay in wait for us.
The oceans surely would swallow us before a rock comes down to smite the planet of it's life.