I've heard there's a rumor saying that lord Buddha was born in Sri Lanka and ancient "Dambadiwa" is not India but Sri Lanka. There's a "sal" tree in Sri Lanka which matches to the exact tree that we believe which was there in the birth of baby prince "siddhartha" . I dunno whether they're true or not I just wanna know whether there's a truth behind it, whether what we believe so far is just a lie?! (Ps not Buddhism but the life story of Lord Buddha)
Prince Siddhartha was raised, according to Buddhist texts, in Kapilawastu (I will not present sources for this as I think this would be undisputed).
The exact location of ancient Kapilavastu is unknown. It may have been either Piprahwa in Uttar Pradesh, northern India, or Tilaurakot, present-day Nepal. The two cities are located only fifteen miles from each other.
The Buddha's birthplace is said to be Lumbini, and it should not be any farther from Kapilawasthu than few days of travel by horse-carriage. So the birthplace must still be in the India or Nepal, even if one discounts the pillar erected by Emperor Ashoka at Lumbini. (The place previously known as Rummindei was renamed to Lumbini when the Ashokan pillar was found in 1896.)
The note quoted above is well cited, and it is evident that although the exact birthplace is unknown, it has been at least reduced to a very small area, thousands of Kilometers from Sri Lanka.
The disputes for birthplaces of religious figures are not uncommon in present day. For example, even though there is overwhelming evidence suggesting that Jesus was born somewhere in Middle East, there are Christian groups who believe that he was born in some place in United States, for example, Alabama.
Lumbini, Nepal has been recognized as the birthplace of Siddhartha Gautama since a stone pillar was placed at the site by the emperor Ashoka circa 245 BCE.
I personally believe that Buddha was born in Lumbini in Nepal through in recent times there are a few small groups in Sri Lanka saying otherwise. I personally would be careful about these movements and groups.