Original(?) older article: https://www.figma.com/blog/desperately-seeking-squircles/

Yes, they changed into squircles with iOS 7 I believe.

I wonder if they were inspired by Meego SwipeUI on the Nokia N9? It was visually quite different from everyone else at the time.

No. iOS switched to squircles because their product designers use squircles[0]. If you extrude a rounded rectangle you get a shape that has harsh breaks in the highlights at the point where the rounded part meets the rectangle part. To smooth this off you need a curve where the tangents are smooth. This is also known as "C2 continuity", and you get that level of continuity by ensuring that the second derivative (acceleration) of the curve has no gaps between points.

Absolutely none of these properties matter for icons, of course.

[0] Or at least some curve with similar tangency properties.

> Absolutely none of these properties matter for icons, of course.

To my subjective eye, squircles often do look slightly better in cases where the corner radius is large-ish.