Hi Jean-Noel Durand,
As far as I know there is no way to recognize which event call a service in a mashup,
but as an alternative you could set a value for a property or a textbox value when ou triggered a "SelectedRowChange" or a "ServiceInvokeCompleted" event, for example, you give value to 1 if SelectedRowChange, and 2 if ServiceInvokeCompleted(here you need create another service to set the value at the time either of the two events is triggered), and then the value could be as an input of the service you will call you could set a different logic or do different thing based on the different value passed in.
Hope this helps,
Br,
Anna