This is what you want to see on your Linux router/load balancers' ethtool output.

Is this plain Linux server without any accelerator/FPGA for data plane?

This is a load balancer. The NIC is of course doing a lot of the hard work and that's all ASICs. But then just a lot of CPU threads (~1 per Gbit/s) on a modern PCI bus. Pretty amazing how powerful the most recent generations of hardware are!