hAP Mini and cAP lite have the same CPU (QCA9533) but different architectures (SMIPS and MIPSBE accordingly) - how come? Aren't those hardware architectures?

It may be the same MIPS architecture, but SMIPS could be a Small / Stripped-down build for cheapest devices (RB931-2nD, RB941-2nD) with removed support for most other hardware, to work with very limited resources (only 32 MB RAM, 16 MB flash). Could also be built with different compiler options, like optimization for size instead of speed (the usual default). Just guessing.