It was posted on Oct 29th/30th on every major gaming website. Gamingbolt, Dualshockers, popular social media influencers on Twitter etc ran rampant that day. They even said they reached out twice to Ubisoft and confirmed that XSX was native and PS5 was upscaled. It sparked this now locked thread on it as well.

https://gamrconnect.vgchartz.com/thread/243697/assassinrsquos-creed-valhalla-runs-upscaled-4k-60-fps-on-ps5-xbox-series-x-native-4k-60/1/

Since the PS5 gameplay was shown last week, all the major articles have been updated just to reflect the upscaling part and they redacted the native XSX info after the fact.

https://gamingbolt.com/assassins-creed-valhalla-runs-at-upscaled-4k-on-ps5

https://www.dualshockers.com/assassins-creed-valhalla-ps5-xbox-4k-60fps/

I didn't see Ubisoft make a false claim in this regard. But what happened on our forum at least was that @DirtyP2002 made a thread with the headline that this game runs at native 4K on SX, and upscaled on PS5.

The problem was that in the article he provided, while the Ubisoft representative said it would be upscaled on PS5, he did not say a word about the Series X version.

The article even emphasized the uncertainty of the Series X version. Don't know why DirtyP2002 assumed that this confirmed that the Series X version would be different. When called out on it, he just linked to another article that also did not specify this. So that's why @Ryuu96 locked the thread.

But I think this is a good example of why reading comprehension is important when interpreting what is said in interviews. Especially when making threads with eye catching headlines.
This also reminds me of the list of Ubisoft backwards compatible games on PS5 that @shikamaru317 posted where they were briefly listed as "not backwards compatible on PS5", and then they immediately took down their article citing 'inaccuracies'.

My guess was that someone at Ubisoft saw those games listed under "BOOTABLE - When playing on PS5, this game may exhibit errors or unexpected behaviour and some features available on PS4 may be absent", and assumed this meant they were not playable.
And as it turns out, every one of those games are in fact playable on PS5, and Digital Foundry were unable to find any issues in them. The 'unexpected behavior' could simply mean that they haven't been thoroughly tested yet, or there could be a few pixels that are off somewhere, 30 hours into the game, etc.

I also wanted to point something out to @sales2099 in the "Valhallah is not native on PS5" thread a few weeks ago, but I'll do it here instead.

It's fine to pop off and be happy if that were the case. But it's also important to make sure to read and understand the source of that information first, or end up in a situation like this. A not insignificant amount of people spent time having to correct people on things they really shouldn't have needed to correct them on, if those people just understand what they read.

And a lot of times they don't. So we've had an influx of misleading, to straight up false, assertions in thread titles in the past few months almost every week.
Which are seemingly often driven by the desire to dunk on on a particular company prematurely, instead of waiting a couple of weeks, or reading things properly first.

One week it's "Series X is overheating." The next it's "PS5 is spying on you." Etc.