Most of the nuts are this way. Pistachio, Almond, Walnut, etc. Nobody actually eats the fruit - just the seed. Mistletoe and Soapnut are also inedible.
Because a fruit holds seeds. It "fruits" (protects) them until the fruit's exterior has been used in some sort of way, and, the seeds are scattered.
All fruits have some fructose, even puckery old persimmons and lemons.
yes
ripened or fermenting fruits and vegetables.