So I figured out why it was showing up as 0 in my MH FFP. Called them and they told me it was a redemption fare class so automatically detected as non-accruing flight. It's strange as I bought it with cash through an OTA, the CS told me it's possible the OTA redeemed the actual ticket in miles but took payment from me in cash (is this legal lol?) But this doesn't explain why the return leg of the flight (also same fare class with the correct BA FFP on the boarding pass) was able to accrue Tier Points and Avios! (CS told me it's possible BA has different rules for crediting flights, I'm skeptical by now)

MH CS told me crediting is non-reversible after it shows up in my account. Guess that's a lesson learned for me to always be vigilant during check-in to check the FFP at check-in.