I could find the correct idea of inserting a different thread, but I do not think that this is the measure that can dissolve my doubts. As I said, it is enough to shield, with a body that can absorb photons emitted by the wire, or a wall face (even if only partially) by the black body. When it is necessary to make a correct flow calorimetry is necessary that the inside of the calorimeter is a black body, and the temeprature of the inner wall should be as low and as constant as possible. For this the calorimeters are made with metal and with the inner wall possibly burnished and externally must be completely covered by a jacket of water (or other fluid deemed appropriate for the test). The cooling fluid must flow quickly enough in order to prevent the temperature to rise so as not to affect the test. In this case, I mean the first experiment seen in the movie, I think it is sufficient to insert a steel tube that surrounds but does not touch, the quartz tube. Obviously this is a calorimetry absolutely primitive, but if the values of the temperature with the filling of air and after hydrogen tend to approach, then this explains the mystery that ultimately would not be a mystery, but only a measurement error
Another possibility is to do a test with helium (instead of air), but I do not know if this is in the lab ... you can always buy from those who distribute gas in cylinders for industrial use, or get the tanks used to charge the balloons (but beware that it is pure helium ...), but it seems this approach complicated when a simple metal pipe can approaching to the experiment to a real calorimetry.