lol! No, it's not a mutant. If the plant is a seedling, that will be its first mature growth--the first that will very likely bloom. Mature divisions of bifoliates will very often do something similar on their first or second growths after having been divided. They'll come up with a PB that only has one leaf which will rarely produce a spike. Subsequent growths--assuming good care--will develop the regular twin leaves and will produce. Nice going: it sounds like the plant is on its way!