Before making any firm judgements it is perhaps worth considering how reliable the CryoSat-2 derived Sea Ice Thickness is likely to be.
The SIRAL (Synthetic Aperture Interferometric Radar Altimeter) instrument on CryoSat-2 has a footprint of approximately 0.3 km along track by 1.5 km across track and requires 369 days to provide global coverage. So it would require well over 1000 "footprints" to cover a 25km grid cell.
In his original study, Laxon used a 0.4 degree latitude by 4 degree longitude grid, and required a minimum of 100 measurements in each cell. The 25km EASE-2 grid used by AWI is somewhat smaller than the grid used by Laxon, but the 100 measurement threshold would seem to be reasonable.
AWI provide data for the total number of valid sea-ice thickness data points inside each 25km grid cell, which indicate that around 49% of grid cells reporting sea ice fall below this threshold. This in itself does not invalidate those data, but as the random uncertainties of the individual measurements decreases with the square root of the data points inside each grid cell, it is worth considering.
Ricker, R., Hendricks, S., Helm, V., Skourup, H., and Davidson, M.: Sensitivity of CryoSat-2 Arctic sea-ice freeboard and thickness on radar-waveform interpretation, The Cryosphere, 8, 1607-1622,
https://doi.org/10.5194/tc-8-1607-2014, 2014.
https://www.the-cryosphere.net/8/1607/2014/Laxon S. W., K. A. Giles, A. L. Ridout, D. J. Wingham, R. Willatt, R. Cullen, R. Kwok, A. Schweiger, J. Zhang, C. Haas, S. Hendricks, R. Krishfield, N. Kurtz, S. Farrell and M. Davidson (2013), CryoSat-2 estimates of Arctic sea ice thickness and volume, Geophysical Research Letters, 40, doi:10.1002/grl.50193.
http://onlinelibrary.wiley.com/wol1/doi/10.1002/grl.50193/abstract