Chuckula, the GPU is Polaris-based, not Vega. The Geekbench leak says GFX804, which is the naming for Polaris 12. Presumably that's the lower power 65W part.
Use of EMIB means they probably don't need refitting the die for HBM2.
24CU/1536SPs suggest a further cut down version of RX 470/570, more so than the 470D(Chinese only version) that has 1792SPs. The performance should be quite close though, because Polaris at this level is memory bandwidth bound. Benchmarks indicate 470D loses only minor performance compared to the RX 470. The HBM2 modules are said to be clocked at 600/800MHz, which results in 153 and 200GB/s bandwidth. Pretty much on par with retail full Polaris 10 parts.
The reason for not using Vega may be lack of availability, or not enough volume for the version Intel wants.