As far as I know, SBE was designed with financial protocols in mind, though possiblity more order entry (FIX-SBE) than market data. I'm not saying it is the case but it's possible that it's more suited to the IEX market data that the article uses for the performance test than capnproto or flatbuffers.

I will consider it in future though, while I'm familiar with SBE it's not one I'd have thought of when thinking about serialisation.