Just to piggyback on this. The simple truth is that lot of things are just called things because they resemble other things, either in form or function.

Coffee is not a bean; beans come from legumes, coffee fruit seeds are roughly bean sized and shaped.

Cacao and vanilla are also not legumes.

The peanut is a legume like beans and peas, but the it’s fruit treated like a culinary nut.

Cashews are not true nuts. They Grow outside the actual fruit.

Nut milk and butter do not come from mammary glands.

Tea is made for the leaves of the tea plant (Camellia sinensis), which is a shrub or small tree, but many infusions of dried plant matter are often referred to as teas. The Tea Tree (Melaleuca) of oil fame is a different plant entirely. It got its name because some sailors made a ‘tea’ from its leaves after they ran out of real tea leaves.

Currants (genus Ribes) are actually named after raisins. Raisins of Corinth were small raisins that were produced and exported from… well… Corinth. Over time ‘Corinth’ morphed into ‘currant’, they dropped the ‘raisins of’, and the local small dryable fruit started being referred to as a currants too. Eventually, production of the tiny raisins migrated to other parts of Greece and some smart guy thought “Hey! Let’s market these fancy tiny raisins that we are importing from Zante (the greek island Zakynthos) by calling them Zante Currants to distinguish them from the common local currants.

Interesting, but the all-knowing Wikipedia seems to agree with you:

From https://en.wikipedia.org/wiki/Coffee_bean:

Even though the coffee beans are not technically beans, they are referred to as such because of their resemblance to true beans.

I’m still tempted to try this, though.