Shoots galore!

When a winemaker/grower friend recently asked me if I had ever seen both the primary and secondary shoots push on a grapevine I answered, "Yes.  And even the tertiary bud occasionally".  She seemed a little concerned that something was amiss in her vineyard as she hadn't really witnessed this phenomenon before.  I, on the other hand, deal with this vegetative-merrymaking every year in Vinoland and have, in the past, simply attributed it to the over exuberance of certain vines.  One such Cabernet sauvignon vine, sporting all three shoots, posed for the above photograph.  But it did get me thinking.
After a quick shufty through all of my viticulture books with no satisfactory findings, I turned to the internet - not much joy there either I'm afraid.  The conventional wisdom online is that the main reason for a secondary shoot pushing is the death or removal of the primary shoot.  Call me old fashioned, but I think the primary shoot in the photograph looks very much alive.  The second reason is perhaps that the vine has suffered a severe pruning.  Nope, I prune the same every year - 2 eight-bud canes and 2 two-bud spurs (5' by 7' spacing) which, in my opinion, is not that severe.  The third reason given is boron deficiency.  Ha!  Coombsville is known for boron toxicity: a neighbour of mine even trucks in water for their vineyard because their boron-rich well water would kill their vines. 
Not being happy with any of my findings, my last resort was to email Dr. Stephen Krebs, my VWT professor at NVC (who, I just found, out is retiring this summer and I am just devastated by the news).  If there is one, ultimate viticultural-brain to pick then Dr. Krebs is in possession of it.  And he said; 
"As for the multiple-bud push, the only explanation that makes sense, of the ones you listed, is severe pruning (which translates to “over exuberance”). If you combine that with a lot of soil moisture and warm, sunny conditions at bud break, I think you get many doubles and even triples."
And there you have it, at least I am satisfied with that explanation.  The climatic conditions at budbreak were such that all of Vinoland's vines were invested with a natural exuberance - which translates as a lot of suckering and thinning in Vinogirl's near future.  I love vines.