It’s a small thing, I know. But when I order something from a menu, I expect to get what is described. If I order a sandwich and it unexpectedly shows up with mayonaise all over it, that’s going right back to the kitchen. If I had wanted mayonaise, I would have ordered mayonaise.
This is surprisingly common with desserts. For some odd reason, any establishment that wants to look upscale can’t resist serving anything chocolate without a criss-cross pattern of rasberry sauce all over the plate. Look, your menu said “Layers and Layers of Fudge Cake with Chocolate Truffle Cream and Chocolate Mousse”, it didn’t say anything about putting red sauce all over everything. If I had wanted red sauce, I’d have ordered it. Don’t make me feel weird for sending back dessert.