Tartine Country Bread Mistake

I had an odd experience yesterday making the dough for Tartine Country Bread.. I normally us KA AP flour - because I think it yields a softer textured crumb - I had found that using KA bread flour was easier to work with - but once I got more comfortable with slap and fold, etc. - working with all purpose was fine.  I had some bread flour left over that I wanted to use - so I used it and 10% wheat flour with the standard recipe yesterday.  I do the initial mix in a spiral mixer.  What was odd, was that during the initial mix, the doug came together unusually quickly - in less than 3 minutes of mixing I had a very cohesive ball.  A let it autolyse for about 25 minutes and then added the salt (Black Diamond Kosher) and 50g more water to bring the dough to 75% hydration.. Usually when I add the water and the salt, the dough comes apart and then comes back together... this time - the dough stayed in a cohesive mass (one chunk broke off - but stayed as a separate piece (still using spiral mixer)).  I added 50 more grams of water (now 80% hydration) - but the dough didn't really come apart. To avoid over kneading, I turned off after 4 minutes and put it into a large plastic tub that I always use for the bulk ferment.  The dough already felt developed at this point in terms of elasticity - also strange.  I then ended up having to go to an unexpected appointment after the first turn (30 minutes into the bulk ferment).  Because I was going to be gone for several hours, I put the dough in the refrigerator to retard the bulk ferment.  I was gone for about 3.5 hours - when I returned, I completed the 2nd turn.  Again, the dough already seemed to have very high elasticity and the texture was like a fully proofed dough.  At any rate, i did two more turns and then did the initial shaping about 5 hours later.  During the initial shaping, the dough had high elasticity and essentially maintained it's shape as a ball (never had that happen before).  30 minutes later I did the final shape and again put the dough back in the refrigerator and then slashed and baked it about 7.5 hours later.  here is the result. It's been quite dry in Northern California where I bake - I'm not sure if that's why the flour absorbed so much flour so quickly - but the bread turned out surprisingly well given all the timing errors through the bulk ferment and the final proofing.  The crumb texture is also remarkably tender for using bread flour.. I'm a bit confused about why it had such significant oven spring.