"Good night Malaysian three seven zero"
A perfectly normal and routine and curtious signing off, nothing more can possibly be imputed.
What remains to be revealed are;
The full ATC transcript and how busy the KL airspace was at the relevant times.
Did the aircraft re enter KL TMA, the radar services charts and all KL FIR info may be found at the following link.
http://aip.dca.gov.my/aip%20pdf/ENR/...1.6/Enr1_6.pdf