Usage of “jealous of”

Stephen Fry in his book Heroes describes how Gigantomachy started, by stating that Alcyoneus stole the cattle from Helios.
The passage goes as follows:

“The sun god Helios was jealous of his fine herd of cattle. Their theft by the giant Alcyoneus proved the final provocation…”

Which, as I understand it, implies that Helious was widely known for his cattle, thus OTHERS were jealous of SAID CATTLE.
That’s where the confusion lies, because in the sentence above it is worded as if Helios himself was jealous of his own cattle.

I cannot seem to find a similar example of this usage of jealous, so maybe I’m just understanding it wrong?
Would appreciate an explanation for this!