Neither did I, however since shrimp genetics are still mysterious, and more and more halfsiders are becoming common in Europe- it's beginning to look like inverts may be able to have some kind of genetic coloring disposition emulating (or indeed real) chimera.
True chimera are two different embryos that failed to split. Twins in one body so to speak. Who knows if it works teh same way in shrimp.
I know of an experiment that took a halfsider x TB, and wound up with 30% halfsiders. So genetics of this look pretty promising.
To find out conclusively if this was chimera, each side would have to be tested and the genetics compared. If each DNA side is different, then it is true chimera. If not, then we know it is some kind of coloring issue.