In their latest communication the airline said "The authorities are looking at a possibility of an attempt made by MH370 to turn back to Subang" (my italics).
The plane didn't originate from Subang, and if this is more than speculation it explains why they're focussing the search on the west side of the peninsula.
Might be referring to Subang Center ATC. IIRC the flight was in contact with Subang Center when it disappeared, but close to handover to Ho Chi Minh Center. So the statement above may simply mean that the flight might have been trying to return to Subang Center airspace rather than anything more profound/sinister.
Besides, Subang is essentially KL.