First of all, MST is not magnetic swipe transaction.

MST is a technology acquired by Samsung, Magnetic Secure Transmission, a technology that simulate magnetic wave so that the conventional magnetic card used to swipe on the side of the terminal. U cant find this in ApplePay or AndroidPay if the terminal do not support paywave they cannot be used at all.

Secondly, BNM did mandate Pin&Pay, all cards issued in MY have to be complianced and no magnetic swipe allow for physical card transaction, u can try to swipe ur plastic card on the magnetic swipe area u will see terminal prompt u to insert card instead. (understand this, u can swipe, just that terminal prompt u to insert card)

Now the fun part: if the card is pure magnetic card only, when u swipe, u will see the transaction will go through and not asking any PIN. This will happened if u using foreign card non EMV standard.

Now, to clear ur doubts on this Samsung Pay on MST.
1. Swipe MY plastic card, track2 data captured will tell terminal this is chip enabled card, therefore terminal decision: Prompt to insert card.
2. Swipe foreign non EMV card, track2 captured will tell terminal this is non chip card, proceed if the terminal allow magnetic transaction.
3. "wave" with samsung pay using MST, terminal will read this as "non chip presented", and therefore proceed as usual, macam scenario 2.
My wild guess