This is the 7101st most frequent Polish word.
hülyi
The word "hülyi" is not Polish; it is Hungarian and means "stupid" or "foolish" in English.
Here, 'głupi' is similar in usage to 'hülyi' in Hungarian, indicating someone lacks intelligence or is naive.
On nie jest głupi, tylko taki trochę niezdarny.
He is not stupid, just a bit clumsy.
In this sentence, 'głupia' modifies 'pomyłka' to express the mistake was minor or inconsequential, akin to 'hülye' suggesting something trivial or foolish in Hungarian.
To była głupia pomyłka, nie przejmuj się.
It was a silly mistake, don't worry.
Here, 'głupi' is admonishing someone lightly for their impractical idea, much like 'hülye' could softy criticize in Hungarian.