I learned Japanese while a friend of mine learned Korean. We would talk sometimes and teach each other languages. One thing I grew envious of was hangul. It is such a drastically better writing system than the Japanese system of kana and kanji that it isn't even funny. It really makes writing Japanese feel hacked together.
The Japanese writing system uses different letters for the same sounds, depending on their source - foreign languages and animal sounds use Katakana, not Hiragana. If it were intentional, it might be considered rude to foreigners to organize a language that way - grouping foreigners with the animals, based on their sounds.
Please note that Japanese words themselves can also be written in katakana, sometimes as a sort of emphasis. Other reasons can be it being a brand/name, or because it is easier on the eyes, or because the kanji are too difficult. So it's not like every word written in katakana is a foreign one.
That said, most words written in katakana are probably foreign.
