Reliability: Were the experiments repeated? Were the results consistent?
Accuracy: It is most likely inaccurate as the test was invalid (see below), also, the result is relatively inaccurate when compared to actual values.
Validity: The experiment relied on the fact that it would occur in ideal conditions but it was not. There are many sources of error such as incomplete combustion as seen by the yellow flame and hence, lower heat released, impurities in the air causes different molar heat of combustion as other substances such as nitrogen oxides can also form etc.