Here is how this Chinese processor claims 512 (single precision) GFLOPS: each core seems to have 128-bit NEON vector instructions, so it can execute 4 32-bit operations per cycle. The core runs at 2 GHz, so that's 8 GFLOPS per core. Times 64 cores = 512 GFLOPS. So yeah their claims check out.

These benchmark numbers you found about the Exynos 5433 are so low probably because "Geekbench 3" is not very good at reaching the maximum theoretical performance, as it runs a bunch of real-world computing tasks. In general you need to hand-code assembly loops of fused-multiply-add instructions to reach the max theoretical perf and clearly this is not what Geekbench does, look at the list of FP workloads it runs: http://support.primatelabs.com/kb/geekbench/geekbench-3-benc...