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.
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.