Indeed, good measured performance.
Also, if I read the graph correctly, the highest phase angles occur at or near impedance peaks. This may help, but still and all, 60 degrees is pretty brisk and corrosponds to a power factor of 0.5 (Cos 60) which means that at that particular frequency, only half the amplifiers power is available to do actual work. This occurs at a frequency range in which there is substantial musical energy.
In general, I prefer the Smith Chart for this presentation, since you can easily see displacement from the horizontal axis as phase angle data.
As a matter of fact, simply speaking from a measured / electrical aspect, this is indeed a somewhat demanding speaker. Good watts are a must.
If you were a Chemical or Mechanical engineer, you have a good reasonable excuse for not knowing about PF and phase. I work with a bunch of EEs, in a semiconductor manufacturing enviroment. At least one of 'em NEVER forgot anything he ever saw in a math class@!!
But the math is pretty straightforward. Most audiophiles get hung up on impedance and you can't talk 'em out of it!
I used to drive a Baracudo.