They're probably generating the level with the seed. I don't think it's very useful, other than testing on their end (so they can check afterwards what the level was).
You could be right, but I think the seed is a lot more interesting. If you simply wanted to generate the level, you could use a random number generator on the device and wouldn't care about logging it.
As you showed by varying colors, the candy distribution determines how likely the player is to win, whether they fall just short of clearing the level, etc. This will have a significant impact on whether they pay to continue, buy boosts, etc.
They may not have done it at launch but as more and more people play and they collect the stats for each seed, I'm sure they can track how easy / difficult each seed is and send the seeds that they wish to do whatever objective they have.
Most of these F2P play games collect and analyze an insane amount of player activity and have sophisticated analytics that they then analyze to make the game more addictive or to increase player spending.
By the way, if you liked this, there are more posts in that series: http://www.stavros.io/series/winning/