So, I was reading a commentary about an illustrator and it said :
ツノと緑が大好きです
Does this ツノ really mean horn?
It's strange, so I'm kinda curious.
Yes, it's simply 角【つの】 ("horn"). Some people actually like it (I'm not sure, but maybe as a variation of ケモ耳 fandom)
Many native Japanese words are written in katakana for various reasons. In this specific case, the kanji 角 can be read as つの ("horn"), かど ("corner") or かく ("angle"), depending on the context. Writing it as ツノ is a fairly common approach to avoid confusion.