[mrcceo]

I brewed an ESB yesterday and as part of the process I used Kai’s fast fermentation test.  Much to my amazement after letting the test ferment for 24 hours I noticed that an incredible amount of yeast formed on the bottom of the test flask.   
In proportion to my normal starter it appeared to be about triple the yeast production rate.
 
I use DME, yeast nutrients, and O2, for my standard starter .  SG of 1.040
The wort for the ESB was an all grain recipe.  SG of 1.052 IBU’s = 34.  Added yeast nutrients & Whirlflock,  No O2 for test sample.
The water for the starter is boiled filtered tap water.   Ca-32, Mg-10, Na-33, So-14, RA-33
The water for the ESB was adjusted to:  Ca-69, Mg-10, Na-65, So-87, Cl-67, RA-81

Any opinions as to what single factor caused the dramatic increase in the yeast growth, or was it a combination of all of them?

[a10t2]

Was it the same strain of yeast and the same pitching rate?

[mrcceo]

It was the same strain. (Wyeast 1318)
I can't be sure of the pitch rate. It was the thin film that was left at the bottom of the flask after I pitched the yeast.
Since I was only inoculating 150 mls of wort for the fermentation test I figured it was plenty.