Swift was developed in secret and launched to unsuspecting public in near 'complete' status in 2014 then a 1.2 version quickly followed. Now it is version 2.0 after one year of launch. That is some serious version inflation.
Kotlin was developed in the open from much of its development and you can see how the language evolves based on the feedback of early adopters. There is no rush to 1.0 until they feel they got the right mix of features.
I just think the way Jetbrains approached the development of the language is more responsible and it bodes well for future iteration of the language.
I just started learning Swift, and I keep running into stackoverflow answers saying "Here's how it worked in 1.0. In 1.2 you have to do this instead. But in 2.0 you do it this other way."
I would imagine based on the context of the sentence, that as JetBrains are taking their time with the language, they aren't rushing through developing it further and making mistakes etc.
For me, the swift language is becoming dangerously like Scala. It's becoming a really large language syntax-wise. Trying to incorporate too many features.