Trad Caths have their own conspiracy theories around Merton's death, that it was a kind of divine chastisement.
I'm just willing to leave it as a tragic accident or mystery.
Dabbling in eastern religions was the least of Merton's "sins", if you can even call it that (by modern post Vatican II standards, it really wasn't). Like the affair he had with a nurse, for instance.
In the end, it just shows that Merton was deeply human, though, and I think he would be the first to admit that. He went into the monastery wanting to escape "the world", wrote a popular book about the grandeur of monastic asceticism, then came later in life to realize his relationship with monasticism had to be much more complex, because he was becoming something more than just a silent Cistercian monk. The more he retreated from the world, the more he felt drawn back into it, on a deeper level. Authenticity and growth, and spiritual bypassing, just don't go together. They are like oil and water.