He's using Strike for 2 reasons (at minimum).

1. Minibits uses lightning and Proton Wallet is an on-chain wallet. He's using strike to trade sats on lightning for sats on-chain.

2. Strike offers free on-chain withdrawals, so all he has to pay is the small lightning transaction fee to send the sats to Strike, and then Strike covers the on-chain fee for the withdrawal to Proton Wallet.