K4 has been tested several times before, including from Arihant. I suspect this test was carried out by the new and improved S4 Aridaman as part of her sea trials.
K4 is our 1st gen full-size SLBM that entered development in the 1990s when our missile tech was still evolving. So nose ejection is par for the course.
The new K5 will be the one to watch- all composite stages, Trident/m51 style aerospike, MIRV and likely gas ejection.

