Yes and no.
First, when you are calculating the capacitive reactance, consider what capacitance you are interested in: the capacitance to the hot wire only, or the capacitance to everything including neutral and ambient ground in parallel with the capacitance to the hot wire?
The voltage on the cabinet when floating is below the line voltage as a result of a voltage divider comprising the capacitance to hot and the capacitance to neutral/ground. When you connect the ammeter to ground, you are effectively grounding the cabinet through its very low resistance, shorting out the stray capacitance to ground and measuring the current when the full line voltage is across the capacitance to hot. Therefore if you are specifically trying to find the capacitance to hot, the relevant voltage is the 120V supply voltage, not the voltage measured on the cabinet when floating. Using the latter voltage will give you the source impedance of the touch leakage but this includes the reactance of the stray capacitance to the world outside, which although real is not part of the electrical equipment.
As it happens, the measured O/C voltage is about half the line voltage, so the two capacitances, to hot and to neutral/ground, are similar, and the result differs between the two scenarios by a factor less than two.
1.2mA is a 'sane' value for the touch leakage which could give you a noticeable but not painful sensation.
Using 120V we get Xc=104kΩ and C=25nF or using the measured voltage we get 46nF as per your calcs.
This is a high value for cable leakage, corresponding to hundreds of feet of NM cable with a ground conductor present but not grounded. Yet you describe the circuit as not having a ground. This kind of value is high even for suppression capacitors from hot and neutral to ground, although such a scenario would also account for the near symmetry that is causing the voltage on the cabinet to lie close to the midpoint of hot and neutral.
Is it possible that the cabinet is connected, via say the ECG in a 3-conductor cord to a 3-prong duplex outlet shared with an appliance that contains a suppression capacitors? If the outlet itself does not have a connection to ground, leakage produced by the appliance could be present at the cabinet.
Another consideration is that if the LED driver is leaking to the cabinet at frequencies other than 60Hz, both the measurement and the calculation could be invalid. However this would not typically result in over a millamp of leakage.