If you press enter many times you can answer (Yes/no) questions before you are presented with the question. Tested this on Ubuntu 20.04 with both tl-4.12.1 and tl-4.13.0.
I did this by pressing and holding enter key during a step in the installation that took a few seconds. Then released the enter key after a second or two. The result is that all following questions are answered with "yes" without me touching the keyboard.
Maybe a more realistic scenario is that the user accidentally presses enter two
times fast in a row, or holding enter for a bit too long. This can result in ThinLinc doing changes to the system that the user did not actually approve.