Incidentally, if his flute had measured 1.7 meters, he could have fitted it across the diagonal of a box whose sides were 1 meter long. The diagonal of a cube is the square root of the three times its side -- 1.73 meters.
From a theoretical mathematical viewpoint, there is no reason why this process cannot be extended indefinitely. If Boris could construct a four-dimensional box with 1-meter sides, then he could get a 2-meter flute in it (square root of 4) and a 25-dimensional construction could contain a 5-meter flute while still meeting the rules of having no side longer than 1 meter.