I am continually surprised to hear people use has and is interchangeably.
The erudite Peter Segal has been guilty of saying:
This song is been written by XXX.
YY is been a producer on the show ZZZ and now lives in California.
Should the two sentences use has since they refer to events in the past?
Are is and has really interchangeable? If so, under what circumstances can one be substituted by the other?
They are not interchangeable. What happens is that the contracted forms of has and is sound the same in sentences like:
He’s been doing that for years.
(He has been doing that for years.)
He’s not a doctor.
(He is not a doctor.)
In your example, I think he might have said:
This song’s been written by XXX.
(This song has been written by XXX.)