Well, not all pies are desserts for sure, but a tomato pie is, unless you deviate from the usual recipes.

Besides, you didn't say that a dessert has to be a cake.

There's also tomato jams, compote, and you can do a tomato cake mind you, a tomato cake is really more like banana bread, where it's a flavoring more than the star of the show.

Point is that tomatoes can definitely serve in the same role as "fruit", just like some things that are sweeter can be used in savory dishes.

It's about the preparation, not the ingredient. I mean, look at bacon jam. Not a dessert, but it's a savory and sweet spread that's used in the same was as fruit based jams. Onion jam is in the same range (and, as a side note, there's also onion and tomato pie which is more of a savory dish than a dessert, despite being fairly sweet anyway).

From a culinary standpoint, there are few ingredients that are fully excluded from dessert territory by virtue of having strong savory taste. There's also not many excluded from entrees purely because they're sweet. It's all a wonderful spectrum of sweet and savory