The Arabic is incorrect, but the intended meaning is clear.

The verb نحل means to make up material and falsely add it to a body of work (usually for the purpose of proving a point). The noun is نحل, not انتحال

On the other hand, انتحال means to falsely calim authorship of material produced by others. This is not the intended meaning, but you can forgive the writer.

The code expression أهل الباطل refers to all of those who do not belong to the group that the writer considers to be أهل الحق. The latter is reserved for members of the sect of which the writer approves. Members of all other sects, by default, would be considered أهل الباطل

The idea is that members of heretical sects make up material and add it to the body of Hadith in order to prove their false doctrine.

Note that انتحال can also mean adopt or embrace, which would also fit in with the context, especially if you add ...supposedly ascribed traditions of the Prophet (S). So choose what would most be appropriate for you.

The Arabic text is totally correct. انتحل here means "embrace"
2."اِنْتَحَلَ مَذْهَباً جَديداً" : اِنْتَسَبَ إِلَيْهِ، تَبَنَّاهُ، اِتَّخَذَهُ. "هَلْ صَحيحٌ أَنَّهُ انْتَحَلَ عَقيدَةً جَديدَةً" from Almughni.
this clearly explained in the part " أن يلصقوا به من المحدثات و المبدعات ما تأباه الطبيعة"
means they embrace the Religion and then behave in away so as to add to it what is not from its nature.

باطل means here, something Invalid, vain, false....