Strange... If you slip in the shower and bump your head or trip and fall and bang your head on a desk, you presumably don’t crack your skull on the front AND back AND side. That does sound more like a car accident... of if you were skiing and went head-first into tree... or high-diving straight down into a too-shallow pool.
I suppose it’s possible a slip in the shower could bounce him around enough to where he could hit his head in several places. But even if he cleaned himself up, there should be towels with some blood.