[gg80]

It’s still debated if that is the correct etymology. A different hypothesis has “penguin” deriving from the Latin “pinguis” (fat).

[smcl]

Certainly in Czech the two are related:

tučňák = noun, penguin

tučný = adjective, fat

I don't know if that helps determine the origin of the English word, but it's definitely funny to think that there’s a nation which calls penguins “fatties” :D