Seller keeping their BTC after price spike - not confirming

I made a purchase yesterday and just happened to get in at a nice low price. I sent payment immediately via Zelle. My bank confirms the transaction happened immediately. Seller has not confirmed however. In the mean time, BTC has gone up significantly - more than the amount of the security deposit. What is to stop the seller from simply holding on to the BTC, going to arbitration and getting his coins back? The security deposit is less than the amount he has lost by selling to me at the low price - so he is probably kicking himself now. Can the arbitrator cause the intended transaction to actually go through, or only cancel it? I obviously want it to go through.

Thank you,

Seller’s trade amount BTC are locked in a multisig with the arbitrator as well, not just his security deposit, so I don’t think it would be smart of him to not release them, as he could lose his security deposit as well.

I am unsure about the exact procedure in these cases though, but hopefully it will not come to this and this trade will never go to the arbitration in the first place.