Honestly I have never seen it happen, although I havent been in salt that long, but from what you describe and what I have read it sounds like spawning to me. Here is one account of it, and it sounds like you may want to do a water change pretty soon, as the release of the sperm and such into the tank can et up the avaible oxygen in a reef tank which can in turn cause the death of many of the inhabitants. You may also want to add some airstones to help oxygenate the water.
"In March, the bulb-tipped anemones released huge quantities of sperm one night, as they do each year. The next morning, the water looked as if someone had poured milk into it — you could not see the bottom! The fish were breathing rapidly, and several were resting on the bottom. A 50-percent water change was performed immediately, and the incoming water flow was increased. Another air stone was added. Unfortunately, we lost the younger bicolor angel. This occurred for two more nights in a row, but because we left the extra air stones and kept the incoming water flow high, we did not lose more fish. I hate to think what would have happened if this were a closed system.Thus, I tend to discourage people with closed system reef tanks from encouraging a mass spawning of corals, clams or anemones. Unless you can be there when it happens and can predict exactly when it will occur (not impossible, but not easy, either), and unless you can perform massive water changes in a short time, it is a dangerous event to happen in an aquarium."