Does "related of" mean "associated with"?

No, direct decedent of, knowledge wise.

Sorry failed to understand you.

Descendant
The spell checker I used has been tampered with or it has been edited since.

'Associated with' would imply that it had been associated and not directly linked properly.

Very perspective based, given peoples beliefs about it and that very idea...
Very worried about given the weight applied to what happened so long ago, mind you.

it should be "related to"... although "attributed to" would make more sense in this context.

Nobody so far has answered this question properly. One of the meanings of 'related' is the past participle of the verb to relate - to tell or recount (a story or account). The writer of the quoted text is saying that The Christian myths stories) were first related of (told of or told about) Horus.

Contrex has it right.

SELECTED ANSWER!

bravadyo

In Christian myths, Horus was the first that was told?

The writer is alleging that the same stories related (told) by the early Christians about Jesus, were previously told, centuries before the pre-Christian era, by the ancient Egyptians, about their deity Horus. (This allegation is vigorously disputed by many Biblical scholars).

Contrex is right again, by golly.

Except I had hastily edited my post and left "centuries before the pre-Christian era", which is nonsense, it should be "centuries before the Christian era".

A similar sentence or rather statement .. Pertaining to the phrase, might be..

"Two Gods argued the fate of an army, the people below erratically celebrated in all the usual ways, of diverse mischief and worry, the days information they had received, was not related of the battle raging above, or its intensity"..

A further assertion one can make after that statement, is that, had they known .. All aspects, perhaps usual language and civility would be replaced with singular clarity.. Leaving them ignoring the ale, perhaps even to the point it was logical to assert its incorrectness, as noted, to be importantly denounced with that incorrectness. Which may arrive, "It is indeed correct.. yet again we see we are wrong otherwise".

A majority or minority of the army might also be forced by such a situation to be stating "Ahh, yes .. Of course" repetitively... Verbally or otherwise depending on the situation. As is every day for some of us.