Being as it was in the overflow, under a caddy, and doing fine, I am leaning towards some from of Bunodosoma sp.
These nems are NPS, called warty nems even though not all nems classified as them fit into the actual specifics of that type of nem. I have numerous ones classified as wartys, that have none of the warts, but for whatever reason still fall under them. Sadly, there is not as much research into the 100s of varieties that live in/around our atlantic/gulf coast.
Being as it appears to be an NPS nem, it will need supplemental feeding. This is more than likely why it went to the overlfow area. Missed food was caught by it. I feed mine 3 times a week and it is small mysis they get fed. If regularly fed, they will stay put, even in the light.
here are a few of mine for reference. All classified as warty, but only one really fits the bill for being a warty. (classification was verfied by working with a few FWC marine biologist that I know and they agree there is not enough work being performed on them. As they are not threatened and are everywhere you look under a rock, not really a point, in terms of conservation)
Anohter giveaway that they are very cvlose to some of mine is the arrangement of the tentacles. yours does not have the stacked tents of a majaono, the multi-row, stacked and staggered of an aiptasia, but have the 2 rows of tentacles with a slight offset between each row
The one on the hermit is not a hermit nem, it is a warty that decided to live on the hermit lol. It is now wedged under a rock at sand level.