They received several payments to the same address. Each payment is a separate input when you spend them later. This is why the recent updates to the reference client block the relay of extremely small outputs. If you receive many extremely small outputs, they each must be stored separately as part of the UTXO set, significantly increasing the UTXO size. then they each have to be included separately as inputs later when spending them, which can lead to excessively large (in terms of bytes) transactions. As such, the transaction fees necessary to spend such tiny outputs can end up being larger than the sum of the outputs themselves.
Once again, thank you for the cristal clear answer. For some reason I assumed the balance of an address was merged into a single "input", but I understand how not possible it is, now.
