I then went on the blockchain explorer to view the transaction and I am seeing an input that is not my address
I am not familiar with this particular site, but this is not unexpected. When custodial services hold user funds, they don't necessarily keep the funds in a separate wallet per user. Instead, they have one giant wallet with all the user's funds, and a database to keep track of how much of it is owed to each user. For example, this could be a viable scenario:
- User U wants to make a deposit, so the service creates address A, stores it in the database as "A is receive addr for U", and hands A to the user on the website.
- User U deposits 1 BTC on A. These funds are now controlled by the service, but it credits U with 1 BTC.
- User V does the same; the service creates address B, stores it in the database, and hands it to V on the site.
- User V deposits 10 BTC on B. The service now controls 11 BTC. The service credits V with 10 BTC in its database.
- Now V wants to withdraw 1 BTC to address C. The service looks at its entire wallets, which contains a UTXO worth 1 BTC and a UTXO worth 10 BTC. It decides that it is most economical to use the 1 BTC when withdrawing, and does so - despite the fact that this 1 BTC UTXO is actually the result of a payment crediting another user.
When V now looks at the blockchain, they will observe a transaction that seems to come "from" address A, which is unknown to V. This is misleading. The general advice is not to pay attention to "from" addresses, as they have very little meaning except to the wallet that actually creates the transaction. It is also none of V's concern - they get the funds, and that's what matters.
as well as various outputs which include my address as well as other addresses that do not belong to me.
This too, is expected. Transactions are cheaper when they batch multiple payments together. The website may have queued up your request for a withdrawal for a short period of time, during which other users also made withdrawals. It then constructed a single transaction that performs all these withdrawals in one go, saving fees and wallet fragmentation for the service. One of the outputs may also be "change" going back to a new address belonging to the service, if the input amounts do not exactly cover the total amount intended to be withdrawn.