Why does grid::grid.grabExpr try to open an X11 connection, and how can I prevent it?

Question

1. On Linux, run DISPLAY= R, then issue grid::grid.grabExpr(1). This works fine, so grid::grid.grabExpr does not need an X11 connection.

2. Run DISPLAY=XYZ R and issue the same command. I am now getting

   Error in .External2(C_X11, d$display, d$width, d$height, d$pointsize,  :
     unable to start device X11cairo
   In addition: Warning message:
   In (function (display = "", width, height, pointsize, gamma, bg,  :
     unable to open connection to X11 display ''
   Calls: <Anonymous> -> dev.set -> <Anonymous>
   

Why does grid::grid.grabExpr try to open an X11 connection when it does not need one?

Context: some R code which absolutely should not depend on X11 connection fails to run when I shutdown my X11 server, and I would like to make the code robust towards this happening.

Bonus question: Run DISPLAY=XYZ R, then issue Sys.unsetenv("DISPLAY"); grid::grid.grabExpr(1). I am getting the same error. The only difference between 1. and 2. being set variable DISPLAY, why does unsetting DISPLAY not take me back to the result of 1?