I didn't read in to it.
Also the season 8 holdovers were produced along side the first few episodes of season 9. The weird airing order explains it. They still made the last few episodes of season 8 standard definition on purpose to keep them consistent with the rest of the season:
Hello Bikini Bottom has a model sheet dated March 23, 2012:
View attachment 16066
While Patrick Man, a Season 9A episode has one dated January 27th, 2012:
View attachment 16068
There's also a facebook post from January 21, 2012 stating that Johnny Knoxville had just finished his lines for Extreme Spots:
View attachment 16067
My theory as to why those episodes produced later on were still considered part of season 8 other than the aspect ratio; the episodes still signed off as season 8 were written and storyboarded first, I think the production codes are based on the episode's inception, while the episode numbers seen on the wikis are based on when they're complete.