You can switch boing.c to fullscreen using ALT+ENTER.
On my Windows 10 system with an AMD GPU, I can see the occasional tear - to see it better I added a timing while loop in the main for loop to get ~16ms which is my refresh rate, here I can see a crawl line fairly clearly on the ball in fullscreen.
This was still using the same mode as my desktop, where GLFW simply changes the window to remove WS_OVERLAPPEDWINDOW and sets to HWND_TOPMOST. However the GLFW SwapBuffers functons then do not use DwmFlush() but the SwapBuffers function. I also checked with a hardcoded resolution change on line 262 of boing.c.
So for me, on my driver I’m seeing tearing.
The 1 frame delay you mention is odd, I can’t see anywhere in GLFW which would do this other than through the standard double buffering and SwapBuffers with a non zero swap interval. Unless there is some underlying compositing then a 1 frame delay would still see a tear with a framerate not locked to the refresh as it’s the timing of the swap which matters here.
Sadly though I used to work at Intel on the HD4000 a long time back I’m out of touch with what the OpenGL drivers are doing here, though I may have a chance to take a look on a HD4000 at some point.