Actually India is #6 on the SLBM list, the UK also have SLBM capability.
I believe what the article is referring to is indigenous SLBM capability. Only the countries mentioned - the US, France, Russia, China, and now India - have self developed SLBMs. The UK does have a SLBM, but it is the American Trident system. The UK has always been using American built SLBMs since they took receipt of the Polaris A-3 in the 1960s. Thus, India (with the K-15) is the fifth country to have indigenous SLBM systems, joining the US (with several systems, the most recent being the Trident), France (with the M-51 and M-45), Russia (with several systems, the most recent being the Bulava and the R-29RMU2 Layner), and of course, China with their JL-2 variants).
As for Israel ...they do have underwater systems that are capable of delivering a nuclear payload, but these are cruise missiles and not SLBMs.
So the article is basically correct with India being the fifth country to develop SLBMs, and the US, France, Russia and China being the others.
The UK system is US developed. India is 5th to build one of its own.