I'm pretty sure that's a price reduction. I think Soulver used to be either $19.99 or $24.99; Soulver 3 is a price increase (although not unreasonable).
However, it doesn't sync with Soulver for iOS yet. I suspect Soulver 3 will probably come to the Mac App Store once the iOS app is updated to use the new file format.
Are you sure? Looking at my Soulver macOS receipt I did purchase it for $10 in 2012. I can't tell if it was a sale price but would be coincidental to have the same price cut 7-years apart.
However, it doesn't sync with Soulver for iOS yet. I suspect Soulver 3 will probably come to the Mac App Store once the iOS app is updated to use the new file format.