The current implementation is using the cleartool command:

lsstream "%[dstreams]CXp" streamname

which returns the development streams for a stream. If the command results in an empty list, it is assumed to be a dev stream.

This command does not correctly detect whether a stream is an integration stream. You can have an integration stream without any dependent development streams. A better test is to do a cleartool describe of the stream. This returns whether a stream is an integration stream or a development stream.