ringgitplus article confirm that reloading to Boost not counted as online transaction to be awarded cashback.
Refer: https://ringgitplus.com/en/blog/e-wallet/Wh...-E-Wallets.html

Most e-wallet reloads are classified as online transactions, which means credit cards that offer cashback for online transactions are shortlisted; though some banks may exclude cashback from some e-wallet reloads (such as Public Bank Quantum & Visa Signature for Boost, and UOB YOLO for Boost and BigPay).