My speculation:
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EDIT: got mixed up with whose daughter Dominique was, but I think the general hypothesis still holds.
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- Zac was working with Shamji, under pretense of being estranged from mother
- Zac met Shamji's daughter Dominique, and they were friends or dating
- Zac was staying with Shamji's associate Sharma
- Zac's story was starting to show inconsistencies for Dominique and maybe Shamji
- when Zac's mom texted him "sending much much much love", he had a "look on his face" after reading it that caught Sharma's attention, and he asks who the msg was from. Given his estrangement from his mom and family, Zac had no quick answer that wouldn't imply another love interest. In his confusion, Zac appeared to be cheating on Dominique. Maybe he bragged about another woman, misreading how Sharma would react. Maybe Zac looks like some sort of undercover snitch, for which Sharma is hypersensitive.
- In the course of next few minutes, Sharma grabs/breaks the phone, punches Zac in the jaw and locked him on the terrace, and called Shamji, who turned around due to unresolved confusion of who Zac was
- Zac panics. He knows he knows he cannot explain without everything unraveling. He tries to jump to buy time to invent a story. He fails to make the jump.
- Sharma sees him missing from balcony, but doesn't know if he made it to water or climbed down or what.
- Shamji and Sharma don't know what is going on, and can't make sense of what happened.
- Shamji is trying to keep his daughter out of the situation, so is trapped in his lies.