Clearly in an emergency situation it makes sense to shift the testing rules to avoid withholding treatment from patients. Also, the doctors doing the research used an objective test of the drugs efficacy, actual viral load measurement, which allows determination of effectiveness with smaller populations.
As an example, for some other kinds of drugs it is difficult to determine effectiveness without a large and carefully controlled test population due to the difficulty in measuring the outcome. Consider the problem of measuring the effectiveness of an anti-depressant, where the patients feelings are what needs to be measured.
We are not talking about a tranquilizer here, we are talking a drug that may prevent death, if it doesn't you can pretty much know it didn't work. Why withhold treatment from someone who is dying anyway and they know the risk?