Ivor - these pilots assumed and made a mistake - please don't make mistaken assumptions about my experience!
I realise that much of this is on a discreet waveband, and that the culture of US forces is different to the British culture - and I have worked with US forces so I am not unaware of the style of US talk. cvg2iln makes a good point that the lack of professionalism is in opening fire on a target displaying orange with an element of ambiguity as to positive identification, but I would add that professionalism comes from maintaining good discipline in all areas of operation otherwise mistakes and misunderstandings do occur.
Clearly this incident has a number of factors contributing to it, but ultimately the responsibility lies with the guy pulling the trigger.