As another poster explained, this is the standard nomenclature for these form factors. You see it used in, for instance, wallets (bifold and trifold). If you want to break it down, "trifold" doesn't mean it has three folds. It means it
folds into three sections.
The nomenclature refers to the result, not the mechanism.
While bipanel and tripanel would be more precise, this is just the way the word use fell out. If Samsung tried to assign a different meaning to the terms from what's currently used, that would have led to confusion.
See, for instance, the entry for "trifold" in the OED, which shows it's consistently used to mean three sections, not three folds:
trifold, adj.² & n. meanings, etymology, pronunciation and more in the Oxford English Dictionary
www.oed.com
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