A couple of thoughts:
1. Horford is rebounding more this year than last, particularly on the defensive glass. His defensive rebound rate through 6 games is 24.8%, better than his career average of 22% and close to his career season high of 25.0% in his second year. By contrast, his career offenive rebound rate this year would be his career low (4.3%). His last full season with a better rebound rate than he has currently was 2012-13. This could be a small sample size anomaly, but I also wonder if it has to do with the Celtics' team defense - maybe they are not making it as easy on offensive rebounders this year, allowing Horford to rebound more.
2. Kyrie has been a ballhawk in the early going. Right now he is tied with Marcus Smart for second on the team in steal percentage at 3.2% (Rozier leads at 3.5%). Going into this season, his annual steal percentages were 1.8%, 2.3%, 2.2%, 2.2% (first LeBron year), 1.7%, and 1.6%, so this is either a small sample size fluke or a real shift from Cleveland Kyrie to Boston Kyrie. Interestingly, his career box/plus minus numbers are +4.4 (offensive) and -1.5 (defensive). This year he is at +1.6 (offensive) and +2.0 (defensive), both of which are crazy outliers for him (career worst and best, repsectively). I assume a lot of this can be chalked up to sample size or changing team context, although it is somewhat odd that these numbers for Kyrie were basically consistent in his first three (no LeBron) and last three (with LeBron) years in Cleveland.