As long as you functional do an in effect absurdity of the internal is internally irrelevant, I just do it differently.
I suspect the issue here is that you're taking the rhetorical phrase "from the inside" in your OP source too literally (and I'm not even sure it's a good metaphor in the first place). I think the idea that there are fundamental differences between how natural and social sciences are studied is wrong (whether that is actually what your source was trying to say or not).
The core scientific process is the same regardless of what you're studying. Whether you're observing the interactions between galaxies, atoms or people, the underlying principles are the same.
There is a real complication that I think you're kind of touching on, in that everything we think about is going through the filter of our own mind, and we all know how flawed and inconsistent that can be. Part of the reason for the scientific process is to soften the impact of that, having a standardised way in which lots of people can independently review the same evidence and see if they reach the same conclusions.
BTW what is your evidence for what religion is? Because it can't be based on science, because religion is not around us and in the universe around us, so you are not using science according to your own understanding of science. So what are you using, when you claim you know what religion is?
Of course religion is around us as part of the universe. Religion is just human behaviour and humans are part of the universe, so we can observe and study it in the same way we do anything else. It's highly complex and difficult to establish consistent measurements, but that's true of lots of other things too.
My understanding of what religion is is based on observations, my own and those of other people, notably all the people who compile dictionaries and literally establish what the common understanding and use of the word is. It is probably worth noting that just because some religious people happen to do, say or think something doesn't automatically mean that thing is part of religion.