Why did Chrst call the 5,000 strangers "the light of the world" in the Sermon on the Mount?

Because those believers would be the first Christians sharing the light of the gospel with the rest of the world. But He was not speaking to all the 5,000; only to those who believed in Him.

I cannot in all consciousness,award the best answer to any of these replies--because of their tribalism it did not occur to any of them to entertain that he may of meant everyone who was there.

As prior as the verse in Mat 5:1-2, disciples means all those who follow Jesus not only the 12,

and the meaning of the light of the world is the same as the city on the hill and the light not under the bushels and the salt of the world.

The Light, the city, the salt and the candle are the Word of God that is inside a person who accepted and heard it gladly. They who had the wisdom of God.

He called the 5000, or rather, His disciples as this because they hold the light from the Word of God that can bring someone out of the darkness.

"Those who have ears, let them hear." ^^

We don't know that he did that. All we know is that someone SAID he did that, and told everyone that he had first hand knowledge of it even though it was written 200 years after Jesus supposedly lived.

The disciples were gathered round Jesus up that mount. Whether many crowds of other ordinary Jews also gathered round to hear the point is that every one who heard Jesus say that were Jews.

The jewish scriptures told them that they were God's covenant people, set apart from all pagan nations because they were to be holy. By keeping God's laws they were to show the world how to live with God's blessing. That's why Jesus told the disciples (and any other Jews within earshot) that they were the light of the world. They were.

It would be interesting to ask this to its creator, alas he has died since so so many decades ( I guess).