Wouldn’t the SIA68 flight have detected MH370? NO! The Boeing 777 utilizes a TCAS system for traffic avoidance; the system would ordinarily provide alerts and visualization to pilots if another airplane was too close. However that system only operates by receiving the transponder information from other planes and displaying it for the pilot. If MH370 was flying without the transponder, it would have been invisible to SIA68.
In addition, the TCAS system onboard MH370 would have enabled the pilot(s) to easily locate and approach SIA68 over the Straits of Malacca as they appeared to have done. The system would have shown them the flight’s direction of travel and the altitude it was traveling which would have enabled them to perfectly time an intercept right behind the other Boeing 777. Here is a picture of a TCAS system onboard a 777.