nepalese citizen travelling from sydney to india

As you are coming from Australia (direct I presume), you only need a valid Nepalese passport to enter India.

If you had planned to enter India from Nepal (and not Australia), you wouldn't even need a passport. Conversely if your plan is to enter India from China, Pakistan, Hong-Kong, Macau and Maldives, you will require a visa.

As per Bureau of Immigration (emphasis mine)

IDENTITY DOCUMENTS REQUIRED FOR NEPALESE CITIZEN :

I. A citizen of Nepal entering India by land or air does not require a passport or Visa for entry in India.

II. A citizen of Nepal while travelling by air between Nepal and India is required to be in possession of any of the following identity documents to establish his/her identity as a Nepalese citizen:

• Nepalese Passport.
• Nepalese Citizenship Certificate.
• Voter’s Identification Card issued by the Election Commission of Nepal.
• Limited Validity photo-identity certificate issued by Nepalese Missions in India when deemed necessary.
• For children between age group of 10-18, photo ID issued by the Principal of the School, if accompanied by parents having valid travel documents. No such document is required for children below the age group of 10 years.

III. A citizen of Nepal must be in possession of a valid Passport while entering/exiting India from/to a place other than Nepal.

IV. A citizen of Nepal must have a visa for India if he/she is entering India from China, Macau, Hong Kong, Pakistan and Maldives.