It... isn't, though? There's a side-by-side comparison photo of the naked devices in the linked article, and I'm fairly sure from eyeballing it that the AirTag + the smallest of the accessories (the Belkin one [1]) is still smaller than the Tile.
The latest tile is thinner and more flat. You could probably fit it in a wallet but the round shape of the airtag makes it a bit more awkward. Still, I'm sure people will make it work.
[1]: https://www.apple.com/shop/product/HNPR2ZM/A/belkin-secure-h...