YOU SAID:

and that's when he just realized he was wearing underpants for his hands

INTO JAPANESE

その時、彼は手にパンツをはいていることに気づきました

BACK INTO ENGLISH

That's when I realized he was wearing pants on his hands.

INTO JAPANESE

その時、彼が手にズボンをはいていることに気づきました。

BACK INTO ENGLISH

That's when I realized he was wearing pants on his hands.