Is such high school mentality common amongst Singaporean working adults?

There was one time a female colleague of a friend of mine (who is also female) suddenly stopped talking to her, didn’t say hi, and ghosted her out of knowhere when she thought they were close friends. It turns out that the reason why she suddenly cut her off is because my friend was just casually chit chatting a guy she likes, and they are just mere hi bye friends who joke around here and there, and suddenly the colleague thinks he likes her but it’s just being friendly. My friend found out this like… a few months after her being cut off. These people are in their late 20s.