Pound's intent here was to re-implement haiku in Western terms. He thought that the 5-7-5 thing didn't translate effectively, and that the syllable count wasn't the interesting part anyway. He was aiming for a functional equivalent of haiku, using the tools of western verse to build the thing: It's a naturalistic image that reverberates and suggests more than it explicitly says. Or whatever; I don't know Asian poetry well.
Pound was fond of Chinese and Japanese art and poetry. He translated (rather loosely, I'm told) a great deal of Chinese poetry, and his Cantos dwell extensively on China in spots. His focus in the Cantos is mainly on the social order of ancient China (just as the bits about "Bastun" were concerned with another social order entirely), but he was fascinated by Asian aesthetics as well. That's the part we're seeing here.
Don't take "apparition" too seriously; it means literally "the act or process of appearing", and I think Pound was leaning on that meaning more than anything else. Anything beyond that would be gratuitous, and Pound didn't do gratuitous. He didn't use words casually, either. That word sounds right there; another wouldn't. Pound expected the reader to be sensible about it.
Okay, now forget all that: First and foremost, it is beautiful.