Cause ..it's. The omegaverse
If you read it again, you should know that mc was not in a good situation to refuse the man cause he knows that will caught the attention of people around, he knows that the man is going to cause a mess if he refused and that would cause rumors about him and the brother
Also, he believes that the bodyguard "hopefully understands" the situation as we can see how he gave the bodyguard a glance. They know they can't just do anything rash as their enemy is the ml's brother.
MC is being a dumbass in this latest chapter. Why are you following a weird stranger, who is giving you terrible vibes into a damn bathroom without your bodyguard. This level of stupidity pisses me off.