Why do you suppose this organism was initially a identified as a protozoan?

In 1985, a 0.5-mm cell was discovered in surgeonfish and named Epulopiscium fishelsoni(See11.14 page 315) It was presumed to be protozoan, In 1993, researchers determined that Epulopiscium was actually a gram-positive bacterium. Why do you suppose this organism was initially a identified as a protozoan? What evidence would change the classification to the bacterum?