That’s only the second Surah - early on when Mohammed was still trying to talk Jews and Christians into following him. When they don’t, he decides that beheading is a more suitable strategy and the tone of the Koran changes accordingly.
I don't doubt it, but I had heard the Koran is not really in chronological order, that it was compiled by the illiterate Mohammad's scribe Omer, or someone else later, from something like a basket of different scriptures in no particular order, with the titles of the surahs not put on them by Mohammad either.
The point I was trying to make is that they're not even following their own prophet's word on treatment of non-Mohammadans. It just gets worse if he's also said 'behead at will' or something - I haven't read the whole thing.