Khawarij

It is said about the Khawaarij:

فم يُسبح، و يد تذبح
“A mouth that PRAYS,
and a hand that SLAYS.”

They are deluded in religion, seeking nearness to God by shedding the blood of innocent people.

Can the Qur’an become a means of misguidance?

Yes – the Qur’an states:
يُضِلُّ بِهِ كَثِيرًا
وَيَهْدِي بِهِ كَثِيرًا
وَمَا يُضِلُّ بِهِ إِلَّا الْفَاسِقِين
“He lets so many go astray through it,
and guides many by means of it,
but only the wicked are led astray by it!” [2:26].

So God does not allow anyone to be misguided by it, except those who are inherently corrupt/evil.

A good example are the Khawarij, as Ibn Kathir says:

قال ابن كثير في تفسير الآية :قال ابن أبي حاتم: حُدّثتُ عن إسحاق بن سليمان، عن أبي سِنان، عن عمرو بن مرة، عن مصعب بن سعد، عن سعد { يُضِلُّ بِهِ كَثِيرًا } يعني الخوارج.(تفسير ابن كثير)
“And he lets so many go astray through it”, Sa’d Ibn Abi Waqaas said: “This is applicable to the Khawarij.”
[“Tafsir Ibn Kathir”, 1/209].

And the Prophet said:
يَقْرَءُونَ الْقُرْآنَ يَحْسِبُونَ أَنَّهُ لَهُمْ وَهُوَ عَلَيْهِمْ
“They will recite the Qur’an thinking that it supports them, whereas it is an evidence against them.”
[“Sahih Muslim”, 1066f].
https://sunnah.com/muslim:1066f