I dont think you can install your own OS on this, yet? :) , in order to do 25GBPS on ARM, I am sure they are doing some sort of DPDK ( I mean user space networking.). I would love to learn more on how do they achieve 25GBPS on this little arm64.
Almost guarantee that they aren't doing 25GBPS on the arm chip but on the dedicated ASIC.
I know for most of the Mikrotik platforms what gets offloaded to the ASIC and what gets handled by the CPU is a big deal in performance tuning and selecting the correct product for your use case.
I also think they only achieve about 15GBPS on their backplanes of their routers with SFP28, enough to show a benefit over SFP+ but not really full speed.