To proof perjury is oath mandatory

Hi, please take a note of section 191 in the Indian Penal Code:

Whoever, being legally bound by an oath or by an express provision of law to state the truth, or being bound by law to make a declaration upon any subject, makes any statement which is false, and which he either knows or believes to be false or does not believe to be true, is said to give false evidence.

Thus for the provision to apply, the basic ingredient that needs to be present is being bound, either by an oath or legal provision, to provide the truth. In my opinion, the section is not applicable to the case in question.