Why do both /var/log/Xorg.0.log and /var/log/Xorg.1.log exist on my system?

Question

According to the xorg.conf man page, the log file should be The default log file is /var/log/Xorg.n.log on most platforms, where n is the display number of the Xorg server.

Since I only run one X instance, I expect the display number to be 0.

But both files have been modified today, he /var/log/Xorg.0.log seems to be the current log file, since the /var/log/Xorg.1.log ends with the line :

[SSSSSS.MMM] (II) Server terminated successfully (0). Closing log file.

So, in brief, why are 2 log file here?

Annex 1) xrandr output (as requested):

Screen 0: minimum 320 x 200, current 3200 x 1200, maximum 8192 x 8192
HDMI1 disconnected (normal left inverted right x axis y axis)
DP1 disconnected (normal left inverted right x axis y axis)
HDMI2 connected 1600x1200+1600+0 (normal left inverted right x axis y axis) 367mm x 275mm
   1600x1200     60.00*+
   1280x1024     75.02    60.02  
   1152x864      75.00  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   640x480       75.00    59.94  
   720x400       70.08  
DP2 disconnected (normal left inverted right x axis y axis)
HDMI3 connected primary 1600x1200+0+0 (normal left inverted right x axis y axis) 367mm x 275mm
   1600x1200     60.00*+
   1280x1024     75.02    60.02  
   1152x864      75.00  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   640x480       75.00    59.94  
   720x400       70.08  
DP3 disconnected (normal left inverted right x axis y axis)

Answer 1

The xorg.conf man page is right, another X server was started.

In fact I changed the user by accident while unlocking the computer and opened a guest session. This session started a second X server, creating the /var/log/Xorg.1.log file.