It's a 4Mp sensor with a 160 degree lens in front of it - the optimal mode for dash cams is to not use scaling, so the larger sensor area used the larger the field of view captured.
The way they sell these is that the 2560x1080 mode captures more information than the 1920x1080 mode.
This screenshot is a better example:
Basically you can see there that the picture itself is using the full sensor size (2304x1296 in that case) - the bit within the red box is what the camera sees when it's running at a 1:1 mapping without any scaling for 1080p. When scaling is used the entire picture is squeezed down.
On the Marcus 4 and the G90 it looks like they're currently taking the full sensor size and scaling it down to fit the selected size - if they were using the raw data from the centre of the sensor you would see a difference in field of view between all the modes.
The other higher end cameras like the Panorama do not use scaling and it should offer a slightly sharper picture.
That mode is marketed as a selling point but in truth you're not really gaining anything, other than a bit of extra scaled resolution. It's swings and roundabouts really - some people will prefer one, some the other.