I would also ask, What is a Christian?
I'm still amazed at how little the majority of Christians know the bible. But does one need to be an expert in the bible to call themselves Christian? What is the main point? Is it the knowledge? Or is it the application of the central message of Christ?
And choosing to follow Christ doesn't mean, that at that moment, you are 100% full of an understanding of Christ's teachings. I also know Christians who have other ideas about religion and spirituality outside the bible. And Christians don't possess 1 belief about Christ, or the afterlife, or the godhead, and definitely do not possess a singular interpretation of the bible. Some Christians take everything literally and believe the earth is flat. More Christians believe that Noah's flood was global. The point is, that none of these beliefs determines who is or who isn't a Christian. By the same token, one can't say, you must be or believe the same things as someone else in order to be Rastafarian. Like Christianity, its a pathway. But spirituality is making that pathway your own.
So the question is, not how it applies to others but how does it apply to you? Who cares what others are doing in their own path unless its doing some sort of damage to Rastas as a whole or is advocating some false identity.
For example, I personally view Christmas as wrong for Christians to celebrate because it is quite obviously a pagan holy day dedicated to sun worship. However, Christians have turned it into a day of Christian unity that has influenced the whole world to unite in the spirit of that holy day. So who am I to define Christianity in narrow terms? Even though it defies biblical precedent.
I think Rastafarianism is the same way because I think there are many parallels between Jesus and Haile Selassie I. And even like Jesus who did not fulfill the prophecy of the messiah in his time, and people added their own ideas about what Jesus was supposed to be and do, the same has happened to Selassie. This is why people talk about him being a Christian because some might believe he is literally a rebirth of Jesus while others may believe it is a spiritual rebirth. All these things are relevant but the most relevant thing shouldn't be who/what he was "supposed to be (to us)" but rather who he actually was and what he taught. And our respect and admiration should be sincere. Different parts will appeal to different people. Can't fault people for being different or having different priorities.