Not so sure about the "stolen" part. Bitwig code has a completely different code base (Java backend with UI written using Juce), and the sentiment at the time was that a few devs were frustrated by Ableton management rejecting several proposals that ultimately were implemented in Bitwig.
Also the multitake tracks UI that was implemented in Live 11 is basically a (slightly improved) copy of the same feature on Bitwig.
The stolen part mostly relates around the sales and distribution network, less around the code. Basically the sales equivalent of IP theft, and a really huge douche move by their CEO. Makes him very unsympathetic to me. Not as bad as Behringer but close.
Also the multitake tracks UI that was implemented in Live 11 is basically a (slightly improved) copy of the same feature on Bitwig.