It seems it's both; hence the 4th gloss above. Daijirin just points to 黄砂, which has 4 senses, and the first 3 are all about loess.

Well, daijisen does say "現象", as well as nikk. Koj uses "土の降るさま" and then 現象。。Daijirin points to 黄砂, but here's the entry for 黄砂:
（４）中国大陸の黄土地帯の細かい砂が強風で吹き上げられ，しだいに降下してくる現象。春先，日本でもしばしば観察される。霾(バイ)。[季]春。

So it seems that it's really the phenomenon, not the sand itself.

@@ -16,1 +16,1 @@
-<gloss>dust from the Yellow River region (in China</gloss>
+<gloss>dust from the Yellow River region (China)</gloss>

Koj, Daijr

Both says it's the dust; not the wind. Daijirin simply points to 黄砂.

@@ -12,1 +12,5 @@
-<gloss>wind coming from the north of China containing Yellow dust that arrives in Japan in Spring</gloss>
+<xref type="see" seq="1181990">黄砂・こうさ</xref>
+<gloss>loess</gloss>
+<gloss>yellow sand</gloss>
+<gloss>bai</gloss>
+<gloss>dust from the Yellow River region (in China</gloss>

daij