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It's never really a good idea to use religious or cultural terms too loosely, but just know that the author probably didn't do it with any bad intentions. We western readers sometimes have to remember that Korea is ultimately still a fairly conservative country with little personal connection with other cultures and mob thinking is basically the standard. A lot of the ppl aren't really aware of the concept of being culturally insensitive except when it comes to their own. This isn't me bashing on them, but just noting a fairly natural consequence of a country thats demographically very uniform.
The Muhammad quote may or may not be a saying, like how american's commonly use 'jesus christ' without really associating it with the religious name. Its likely that webtoon authors dont always write with the mindset that westerners will read it, and thus are less conscientious of its references.