The familiar number r=0.2 for the CMB tensor-to-scalar ratio is based on the assumption of zero foreground contribution in the region of the sky observed by BICEP. To argue that foregrounds should not be a big effect, the BICEP paper studied several models to estimate the galactic dust emission. Of those, only the data driven models DDM1 and DDM2 were based actual polarization data inadvertently shared by Planck. However, even these models suggest that foregrounds are not completely negligible. For example, subtracting the foregrounds estimated via DDM2 brings the central value of r down to 0.16 or 0.12 depending how the model is used (cross-correlation vs. auto-correlation). If, instead, the cross-correlated BICEP2 and Keck Array data are used as an input, the tensor-to-scalar ratio can easily be below 0.1, in agreement with the existing bounds from Planck and WMAP.
Raphael's message is that, according to his analysis, the foreground emissions are larger than estimated by BICEP, and that systematic uncertainties on that estimate (due to incomplete information, modeling uncertainties, and scraping numbers from pdf slides) are also large. If that is true, the statistical significance of the primordial B-mode detection is much weaker than what is being claimed by BICEP.
map as BICEP, he also included the Q and U all-sky map (the letters refer to how polarization is parameterized), and models of polarized dust emission based on HI maps (21cm hydrogen line emission is supposed to track the galactic dust). One reason for the discrepancy with the BICEP estimates could be that the effect of the Cosmic Infrared Background - mostly unpolarized emission from faraway galaxies - is non-negligible. The green band in the plot shows the polarized dust emission obtained from the CIB corrected DDM2 model, and compares it to the original BICEP estimate (blue dashed line).
The analysis then goes on to extract the foregrounds starting from several different premises. All available datasets (polarization reconstructed via HI maps, the information scraped from existing Planck's polarization maps) seem to say a similar story: galactic foregrounds can be large in the region of interest and uncertainties are large. The money plot is this one:
Recall that the primordial B-mode signal should show up at moderate angular scales with l∼100 (the high-l end is dominated by non-primordial B-modes from gravitational lensing). Given the current uncertainties, the foreground emission may easily account for the entire BICEP2 signal in that region. Again, this does not prove that tensor mode cannot be there. The story may still reach a happy ending, much like the one of the discovery of accelerated expansion (where serious doubts about systematic uncertainties also were raised after the initial announcement). But the ball is on the BICEP side to convincingly demonstrate that foregrounds are under control.