Someone pointed out to me that cucumbers are technically fruit.

This is one of those gotcha observations that is technically true but fundamentally uninteresting.

The culinary concept of fruit vs vegetable is about their sweetness.

There is no botanical concept of a vegetable.

There is a botanical concept of a fruit, but it's about the part of the plant.

It's not that cucumber is a fruit, but that it's the fruit part of the plant.

So in the botanical sense it's like saying "is edible part of the plant the fruit or a different part?" which is obviously uninteresting in any culinary sense.