That graph begins with IE at 60% share and ends with it at 20% share. It indicates pretty clearly that most of Chrome's growth came from IE, I'm not sure how you can interpret it another way.
Look at the slope in the beginning. People would have switched away from IE anyway. The release of Chrome didn't change the number of people switching away from IE, but it stopped Firefox's growth dead in its tracks.
IE6 stagnation was hated by developers and users alike. Growth of any browser came from something-must-be-better-than-this.
FF had the upper hand against Opera, who were still quite the serious contender. I'm sure someone has done a PhD thesis on this, and if not well worth doing on multi-factor influences on market share for web browsers. Very multi-disciplinary too, covering tech, consumer understanding, embedded incumbents, marketing (a big part in Chrome's boom in my opinion).
Chrome's growth came from IE, yet. But at the time, anyone's growth could have come from IE. Chrome did it better and faster.
* I was still using IE6 in a corporate enviornment in 2013. I have friends that still require IE6 on XP in a company because funding for the system upgrade can't be made. The system's not internet facing, not explicitly. IE6 tried to define the internet, thankfully the internet moved on, and would have moved on. FF was at their tails, Chrome sped that.
