Part of it is coincidence: there are two words here. The spanish word for "weight" = peso. And then the Germanic word goes way back, but we get "penny" from the same root that Germans got "Pfennig" and even the Czech got "penize.... the original meaning is so old it's lost. it's a type of coin or money.

Now just add colonial history: portuguese made it's influence on Swahili and India. Spanish too. Meanwhile pfennig turns to pennies and pence. And so we have a common word for tons of currencies.

Kind of like Thaler turned to dollar, shilling, real(crown), pound(libra), all had similarities across borders and cultures. Peso and penny are just two of many similar etymological stories.