He is not being scrupulous. It is exactly what ones reasoning power is supposed to be used for, determining when one is acting or has acted incorrectly. If the above is scrupulous, the only way to not be scrupulous would be to not think about ones actions. We have enough of that already.
There are several reasons why this does not approach serious sin, or even minor sin, but the taking of something is wrong and the OP is correct in recognizing this. How big or how valuable does something have to be for stealing to start being wrong? Doing what is right sometimes requires a lot of personal deliberation that if we avoid due to a mistaken notion of “scrupulous”, we will begin to see only the big sins as that which constitutes “wrong”. Be perfect, Matt 5:48, does not seem to be a relative perfection but a call to holiness that befits the dignity of man as made in the image of God.