Once the BTC gets to your wallet, it's only whoever controls your wallet that can move the BTC somewhere else.
If Coinbase controls your wallet (not you) they can move the coins around as they please, I guess.
Oh, that's probably Coinbase internally moving them based on their own internal needs. But Coinbase keeps track of my account totals so I still have the same amount internally with their system. Got it.
I didn't even think about how they'd use the wallets internally like that. Thanks for the reply and making me realize what was happening.