What is technically considered an attack?

[BurgerBeast]

Edited for clarity. I re-arranged the text.

-- If it is a banana, it is yellow. Lemons are yellow, but are not bananas.
(colours added)

You're absolutely right, here. Now:

Is a buttercup yellow?

Is a watermelon yellow?

Edit: because this is the same as:

-- If it involves an attack roll, it is an attack. Some things are attacks, but do not involve attack rolls.

Is dragon breath an attack?

Is magic missile an attack?

Edit: We don't know in any of these cases without further knowledge because the definition, as provided, is not exhaustive.

-- If it is a shark, it has a fin. Dolphins have fins, but are not sharks.
The descriptive line you so adamantly cling to is not comprehensive.

And cheetahs do not have fins, and are not sharks.

So, "If there is ever any question about whether an animal has fins: If it is a shark, it has fins."

Hmmm... doesn't really answer the question at all, does it?