well this is not easy to answer, partially true, partially not completely right. There are only a few Arahants, whatever few is, they are difficult to find, for they normally do not advertise them as being such. There can be non Buddhists, one exception I am pretty sure of was Meister Eckhart and he was a Christian. It is not the religion that brings about Arahantship, but it is following the path of sila, samadhi and panna. And as a prerequisite the virtues of generosity, respect and gratitude. So anyone, in whatever religion is following this path might attain to one of the ariya stages. You don't need the fourth jhana, but you do need the skills of diving into the state of deep samadhi, where all the five khandhas will rest to work for the time being.
My general motto is let the people believe what they believe, you cannot change their minds, but you can change your own mind.