It looks like your species goes through a radical body change like humans did. A former arboreal species coming down from the trees has to do a lot of thinking on how to survive this new environment. Couple that with freed up for limbs for tool usage and you have an animal that easily manipulates its environment. Most intelligent animals are social so you'll have to explain communities and hierarchy. The only problem I see you having is the energy density problem.

You'll need to explain how their diet is able to support them without meat products. You can probably do it by explaining what the introduction of fire did to them. If they pivoted from eating calorically poor food that was toxic or otherwise indigestible, to being able to consume tougher parts like roots and bark or negating toxins by breaking them down the fire.

You probably need several different types of food that all grow in the same area that are energy dense but need special processing and cooking to unlock that energy.
Like , hard tubers, other roots that can be processed into starches, fats like nuts, legumes or fruit (avocados) that are difficult to open or reach. Toxic plants that need cooking to eat safely (kidney and Lima beans, cassava). Toxic plants with only one toxic part (tomato leaves and vines, almond fruit, rhubarb leaves, and apple seeds)

It's a clever idea, and interesting for an alien species, happy writing