A companion can be a kaffir

From reading Surah Khaf Verse 35-37. The Quran uses the word companion / Sahib on a kafir. I.e. the companion of the believer was an unbeliever.

We read:

And he entered in his garden while wronging his soul. He said, 'I do not think that it will ever perish';
And I do not think that the Hour will ever come, and even if I am returned to my Lord, then I shall surely, get a better place of return than this garden.
His companion replied to him while arguing with him, 'do you disbelieve in Him Who created you from dust then from a purified drop of water, then made you a right man?'

قَالَ لَهُ صَاحِبُهُ وَهُوَ يُحَاوِرُهُ أَكَفَرْتَ بِالَّذِي خَلَقَكَ مِن تُرَابٍ ثُمَّ مِن نُّطْفَةٍ ثُمَّ سَوَّاكَ رَجُلًا