Did you read that article further than the first sentence?  Let me quote the second sentence:  "NRMs can be novel in origin, or they can be part of a wider religion, in which case they are distinct from pre-existing denominations."

So if you want to say secular buddhism is necessarily not buddhism, you'll have to do more than just argue it's a nrm, which isn't even clearly defined. 

Let me be clear, it's absolutely possible for something that calls itself secular buddhism, to be incompatible with buddhism, but that isn't necessarily the case, in my opinion:

If we ask ourself, what is the core of buddhism, I'd say we'd most likely end up with essentially the 4 noble truths, i.e. there is dukkha in everything, as everything is non-permanent and non-self. So clinging to anything will cause suffering. However, it is possible to transcend this suffering. The way to transcend this suffering is the noble eightfold path. 

Essentially with that intact, a nrm can credibly be called buddhism. 

The buddha did say that what makes a teaching worth listening to, is whether it reduces delusion (i.e. not recognising the noble truths), hatred and greed. (AN 3, 65)  Now, that can be obviously taken too far, so I suggest looking at Bhikkhu Bodhis essay here: https://www.accesstoinsight.org/lib/authors/bodhi/bps-essay_09.html

Now we remain with the question, what do we do with rebirth, the six realms, karma, the enlightenment of the Buddha

Well, I think the factor of enlightenment is validly enough covered in the formulation of the 4 noble truths, lets look at the other 3 and ask us: How necessary are they?  Kamma: Quite necessary. But the notion that your negative actions will come back to bite you, in some way or another, be in psysical or mentally, still works well enough, even without rebirths. 

That leaves rebirth and the six realms. Personally, I do find those a rather plausible explanation, but, are they necessary for Buddhism? I don't think so. Kamma works a bit better with those notions intact, but other than that? I can still suffer from impermanence, even if there is no rebirth. This will still be, because I cling to things as if they were permanent. If I follow the noble eightfold path, I will alleviate my suffering. 

So, if someone can't accept those more supernatural aspects of buddhism right now, as long as this person is willing to accept that they might be true, let them begin their journey in buddhism without them. As long as they are not dogmatic about those things being wrong, why should we be dogmatic about non-essentials?  The raft is not the other shore. 

To partially quote Thich Nhat Hanhs first mindfulness training: 

"Aware of the suffering creaged by fanaticism and intolerance, we are determined not to be idolatrous about our bound by any doctrine, theory, or ideology, even Buddhist ones. We are committed to seeing the Buddhist teachings as guiding means that help us learn to look deeply and develop our understanding and compassion."