I'm the creator, and I think you are spot-on. It is my wish that this data will help increase competition/reduce collusion, but until others analyze it we cannot make assumptions about what prices/grocers are doing.
Your point stands, but it wasn't an "instance of collusion on the price of bread in 2015", but widespread collusion on the price bread and other baked goods from 2001-2015 (some say 2017), which was discovered in 2015.
Ideally, the data would be proving this, but I guess my skepticism is the cost of making a claim before the research is done.