Sri Lankan (Ceylon) goverment did see India as a threat and even made 900 000 Indian Tamils stateless in the 1940s.
There exist 3 groups in Sri Lanka which have Tamil as a mother tongue
Eelam Tamils (Sri Lankan Tamils)
Indian Tamils (Brought to the Island by the Dutch and British)
Sri Lankan Muslims (Tamils and Moor)
Sri Lanka have been a place where both Tamils which are Hindus in majorirty and Sinhalese which are Buddhist in majority have had been in various wars for 1000 of years from Sangam times to present.
Tamil Chola Empire
The Sinhalese Buddhist feared India beacuse it was afraid of Hindu Nationalism could make Sri Lanka a part of India, The great amount of Tamils in Tamil Nadu (State in India) could Unite with the Tamil Eelam (North Eastern parts of Sri Lanka).
The Ceylon later the Sri Lankan goverment did also fear the Dravadian Nationalism in India and feared a merger
The Island had always been part of South Indian and local Tamil Kingdoms and Empires like Chola Empire, Pandiya etc and Tamils have always seen Sri Lanka as their own land while Sinhalese as a Aryan Buddhist invaders.
This made Sinhalese to feel insecure which always made them to support all countries which were against India, USA during the cold war, Pakistan during all wars and today China.
Since Sinhalese are orginally from Bengal, Orissa and Gujurat and the great amount of Tamils both in India and Sri Lanka made the Sinhalese be afraid of being annexed to the federal union of India. Sinhalese voiced against when India annexed Goa and Hydrabad and saw IPKF and Indra Gandhi’s as Hindu imperialism which JVP stated in their manifesto. Even today president and Prime Minister Rajapakshe Brothers voiced against India for trying to make Tamil Eelam a seperate state in India or merge it with Tamil Nadu and it wouldnt be long for the Indians to come South.
The unknown war ( Second JVP insurrection) which led to 60 000 Sinhalese dead
It not a shock what all parties have to common is anti India. UNP goverment which was against the Indian intervention and even armed Tamil Millitant groups like LTTE and PLOTE to fight of the Indians. JVP meant UNP didnt have the backbone or the guts to directly fight of the Indians and thats when the second uprising against the goverment began. JVP which was known for internationalism in the beginning transformed as an Anti-tamil organization to get support in the rural areas.
Former President and now Prime Minister and Brother of the current President Rajapakshe which are known for anti West and Anti Indian approch. This was taken during the Tamil Insurgency and Civil War in North East and JVP Insurgency in South.
Ps this is seen from a Sri Lankan Sinhalese view.