@Maik ***********
Of course that is logic.
QR codes are meant to print out, and much better scannable from paper than from a screen.
That you don't follow clear instructions given by Thai authorities who friendly ask to print the visa, and nevertheless got in without problems, does not mean you should give this as an advice to others.
Why not just follow the rules? It is not really difficult is it?
P.S. 3 minutes at immigration is far above average, so maybe your stubborn behavior caused some delay after all...