It's a bit like (though in reverse) how "canine" is often used for the Canis genus (dogs), but is easily confused for "canid" (the Canidae family) which includes foxes and tanukis.
Really there are two sets of terms - culinary and botanical. Botanically tomatoes are a fruit yes, but they are also a vegetable. And in the culinary context you would never use a tomato like a fruit.
The English language is defined by it's usage, and the same word can mean different things in different contexts. Dinosaur is used commonly to refer to Pterosaurs in the "general" context, so a Pterosaur is a Dinosaur in that context. If you were instead a biologist talking in the context of academia then a Pterosaur would not be a Dinosaur.
So while tomato jam is a type of fruit preserve, not all fruit preserves are made of fruits (despite the name).
The whole vegetable push was initially for taxes.
(https://www.goodhousekeeping.com/home/gardening/a20705757/ar...)
(https://www.businessinsider.com/supreme-court-tomato-is-vege...)
Also, the average Joe around the world is really really bad in plant related food classification. Given that a lot of cookbooks are written by non-culinary experts, I would take such culinary information with a grain of salt as to proper naming and classification. Culinary experts do refer to strawberries, tomatoes etc accordingly.
Biology/Botanology: does not exist. Only the definition of fruit is of interest. Thus something that a cook would call a vegetable are classified into finer categories (e.g. leaves, roots etc).
Speaking of which: I've been anxiously awaiting the day when dictionaries finally give up and declare "it's" as a valid spelling of "its".
I'm not sure what it means to use something "as a fruit" in culinary context, but tomatoes are definitely used in many contexts that other fruits are. Tomatoes, avocados, lemons, limes, grapefruits are all used raw in similar savoury salad-y contexts, and there are plenty of fruits that are also cooked with.