I happend to have had several likewise experiences, ill try explain in my own words.
Certainly dont worry, tell your friend that he isnt abnormal and doesnt have the nature of drawing demons to himself. In contrary he is in the good setting if he can perceive these.
Its a demon because your friend calls it that way, he yust didnt recognise what he saw because its new to him and he probably paniced for a millisec. If he see's the same face (or if the same kind of experience happens) next time during kunlun he shouldnt stop but be extremely happy he can see it ! i assume this is the center between the eyes being opend or atleast being powerd, the kunlun does its job.
Dont think he perceived the "demon" with he's eyes hé

although yes it was a lifelike clear image.
If he would of yust let it pass by and did not stop he would of noticed the face or being would leave from itself, maybe another one arises later on but dont worry, it will go by. Dont tell em yet but if he would of yust let it be and even try to look at it better he would of noticed that however creepylooking it may be at first glance .. the beings on themself actually look very beautifull.
There was a notice here on the forum by Mantra that its possible you could see reptile-like beings.
If he really doesnt feel comfortable with these things or isnt prepared then dont push your friend to try kunlun again, give him the times he needs. Its well possible he's mind has trouble with understanding these events certainly if he doesnt have any experience with these subjects. Let is drip trough.
In short: Yes it is scary at first .. no he's not being haunted .. certainly dont push em because he himself has to deal with what he saw and encountered .. however if he does so he will notice the beauty behind it.
If it would be a real demon then it wouldnt go away after stopping the practice or opening he's eyes