The deposit is part of the purchase contract and is paid according to the contract's timing and terms. If the transaction completes, it is normally credited toward the purchase funds. The down payment is the buyer's total equity contribution toward the purchase price, usually funded at completion together with mortgage proceeds and other closing funds.
The deposit can therefore be part of the down payment without being the same thing as the down payment. Buyers should know where the deposit money will come from, when it must be available, how it will be held, and what the contract says about it.