I take the quote to mean that the control box was excluded from the measurement. What do you mean by "the power was measured on 3 phases"?
"Resistor coil power consumption was measured by placing the instrument in single-phase directly on the coil input cables, and was found to be, on average, about 810 W. From this one derives that the power consumption of the control box was approximately = 110-120 W."
p.16
https://arxiv.org/ftp/arxiv/papers/1305/1305.3913.pdf
Is that what you are referring to? What specific concern do you have?
It is quite simple. The power measurements were gotten from the PCE-830 measuring the 3-phase input to the control box. I don't care about how the control box losses are estimated, but I do reckon Rossi + 3 phase = likely X1/3 underestimation of input power, and the coincidental COP of almost exactly 3 supports this hypothesis. Of course, he might have done it some other way...