The answer:
As we see, the case is unambiguous. There are two distinct species, one with a peak absorbance at 450 nm and the second with a peak absorbance at 550. The 450 nm species reacts at a rate of 5 s-1; the 550 nm species reacts at a rate constant of 6 s-1. (Click on images to open a window with a larger version.)

Raw 3D data:
The original data set for the answer above is shown here in the 3D display—this is the "recording" of the chemical event by collecting spectral data as a function of time.

Fixed wavelength trace:
When some of the data are shown in a 2D format and a time trace is extracted at a particular wavelength, no clue as to the 2 rates is seen.