Old Norse is a Nordic langauge, which makes it a North Germanic language, which, in turn, makes it a Germanic language.
Nordic languages (a family of languages) are descended from Proto-Nordic (a language).
Germanic languages (a family of languages) are descended from Proto-Germanic (a language).
Germanic languages are Indo-European languages, which have Proto-Indo-European as a root language.
You are not wrong in saying that Proto-Germanic and Old-Norse are IE languages. But it's also like saying that nickles and coins are currency, it doesn't mean that nickels are not coins.
Nordic languages (a family of languages) are descended from Proto-Nordic (a language).
Germanic languages (a family of languages) are descended from Proto-Germanic (a language).
Germanic languages are Indo-European languages, which have Proto-Indo-European as a root language.
You are not wrong in saying that Proto-Germanic and Old-Norse are IE languages. But it's also like saying that nickles and coins are currency, it doesn't mean that nickels are not coins.