Screen Size

I think what he's getting at is that the C64 mini looks just like it does if you emulate one on a PC, clean, sharp and ultra blocky compared to the real thing on a CRT. Thing is, emulate a C64 on a PC in a small window and that clean, sharp and blocky look can look most excellent, just like a window movie on Youtube. However make that C64 emulator full screen and it will only increase what you see in size from that small window... In other words a PC emulating a C64 at full screen 1080p will look the same as the C64 mini at full screen on a 1080p screen.

It's something you get used too as all people do that have emulated any computer or console from the CRT era on modern hardware. Even a NES and SNES mini suffer with this upscaled blocky-ness. CRT emulation settings try to resolve this but you may not see the proper result at 1080p as the C64 mini and NES/SNES mini's are native 720p. A bit of sharpness is lost when you upscale.

Try sitting well away from the screen if it's too much or use a smaller screen is your best bet.