I always took it as read that it's a charity because of the tax arrangements (i.e. if they didn't benefit from setting it up that way, they wouldn't be a charity at all).
"IKEA" is a network of many different companies. Some of them are registered as nonprofits (not charities) as a tax optimization which is probably what you are remembering. There is also the charitable organization that was mentioned above but afaik that's not for tax purposes.
