Why has Rengar's Affiliation Swapped to Shurima?

No. He is now (or used to be) part of a Vastayan tribe from Shurima. This has been known since the release of Xayah and Rakan along with the Vastaya lore update.

Like Hextech Owl said, Rengar was moved over to Shurima as part of the Vastaya lore update with Xayah and Rakan's release - Rengar was made into a member of the Kiilash tribe of Vastaya, who live in Shurima.

Ever since Xayah and Rakan came out he has been Shuriman. It's where he was born.

A lot of champions that were categorized as "Runeterran" have been moved to a region since the map came out.

Gnar is Freljordian now Ivern is Ionian Kayle and Morgana are Demacian (interestingly) Fizz is now in Bilgewater Soraka has been moved from Ionia to Mount Targon

So on and so forth. It's just a late change made in tandem with the map so that Riot can be certain that their regions are finalized before changing anything

There is a large jungle area in Shurima,so Rengar is likely part of that and unless they turn said area into its own faction,he'll be counted as a Shuriman.

Maybe he is an ascended. Not so fluent with his lore. But could be.

Because no one at riot cares about the story. Or about the people who know their lore.

In fact if you have ever taken any time out of your day to look up league of legends lore, you know less about league of legends lore than everyone else.

Because whatever you found out has been retconned by now. the Vastayan's are probably gonna get retconned too.....