This is just made to look like Windows 3.1 at a glance but there are many small details that are different from real Windows 3.1 (or even 3.0). For example Windows 3.x do not have a 3D shaded button at the top left corner of windows, instead they have a flat button/square with a thin "-"-like rectangle that has a black outline, white filling and single pixel shadow, like a three pixel tall popup menu (which is intentional since in Win3.x this was supposed to be the icon for applications to use if they wanted to have a dedicated control/widget for showing a popup menu).
Similarly, the mouse cursor's triangular part is smaller, the window corners are missing the "connecting" corner lines, the font is different (in Win3.1 all fonts are bold and the space is narrower), the button shadow color is too dark (this was the case for EGA in Win3.x but this is VGA and in VGA the palette was modified to have a less contrasting shade for the bevel colors), the dialog box (from the first image in the three, not linked in your message) uses the resizeable (but corner lines still missing) border style instead of the dialog box style (which is blue with a white inner line), etc. I'm sure i can find more differences if i spend more time on this and look at Win3.x screenshots, but these are from memory and i think you get the idea :-P.
Similarly, the mouse cursor's triangular part is smaller, the window corners are missing the "connecting" corner lines, the font is different (in Win3.1 all fonts are bold and the space is narrower), the button shadow color is too dark (this was the case for EGA in Win3.x but this is VGA and in VGA the palette was modified to have a less contrasting shade for the bevel colors), the dialog box (from the first image in the three, not linked in your message) uses the resizeable (but corner lines still missing) border style instead of the dialog box style (which is blue with a white inner line), etc. I'm sure i can find more differences if i spend more time on this and look at Win3.x screenshots, but these are from memory and i think you get the idea :-P.