Nicely done. I'm not sure the longer stride is "free" speed, but your results show it certainly helps you.
And good idea to start out front. That race has been notorious for walkers lining up in front, and all the congestion in the first mile. Though I'm told they had pace groups (at least for the half) this year, which may have helped that situation, too.
I have read studies that stretchfing does not help speed......BUT, I am horrendously stiff and nonflexible...I could only get withing 16" of my toes when reaching down!!!!....stretched and got it to 13" in 6 weeks or so.....so I do think it helped because I am so terrible in this area...I am going to keep doing it and perhaps do a bit more.
Looking at my result a bit more it was a solid result but no where near one of my best runs when using the age graded formulas.....the world record for my age was 58% of my time. I ran a 5K at 63% a few years back (that was one of my best runs ever considering my age) but I ran 28:20 on a flat course and cold day in November so to run 25:55 was getting me back to some respectability for my age and a vast improvement over a recent result.