It's quite the opposite. When a drug trip conflicts with one's "spiritual practice" is exactly when you have a problem. That seems to be McKenna's problem in this case: he tried to assigning meaning to an experience he had while compromising his brain function with chemicals.

All you really need is to understand that there's no magic involved here. If you deliberately compromise your brain function, you're going to have strange experiences. It doesn't "mean" anything except that you compromised your brain function.