the only one with an UNKNOWN address as the source of the satoshis.
Addresses don't exist. There are no addresses in bitcoin transactions.
Addresses are an abstraction that we humans use to make it easier to talk about the transfer of control over value using a standard set of locking and unlocking scripts.
Bitcoin transactions use a scripting language to encumber transaction outputs with requirements that must be met for any node to allow those outputs to be used as inputs into a new transaction. There are a standard set of such scripts that have been given names (P2PKH, P2SH, P2WPKH, etc).
Rather than needing to use the name of the script and then the data needed to correctly build the script in every conversation where we are talking about transfering the control over some value, we have created the concept of an "address" which encodes all the necessary details into a single string of letters and numbers. Then the wallet software that we use converts that "address" into the appropriate script for the transaction.
There is nothing in Bitcoin that REQUIRES one of those standard scripts to be used. Anyone can use the scripting language to create any script to accomplish any goal they want when they create a transaction. If the transaction script is not recognized as one of the "standard" ones, some block explorers and wallets will identify that script as being "unknown", others may just show the actual script itself, while still others may choose to create a RIPEMD160 hash of the script and present that as if it were an "address". It's up to the block explorer programmer (or wallet software programmer) to decide how they want to present these non-standard scripts to their users.
As long as someone knows how to satisfy the requirements placed by the "locking" script in the output, they can use that output as an input to a transaction where they want to "spend" that value. It doesn't need to be a "valid address", it just needs to be an "unlocking" script that presents the correct data in the correct format.