This is clearly not provable. However, various people have speculated that the Hindu Vimana is a flying saucer.
Most famously, this is in the works of Erich Von Daniken in the 1960s.
However, a much earlier description was put forward by Desmond Leslie in the 1953 book Flying Saucers Have Landed (ISBN: 9780854351800). This presents a more cogent, less sensationalist, argument.
These works have led to a widespread belief that the Vimana is an interplanetary craft, Indra's Dart is a thermonuclear weapon and other modern interpretations have been put on the technology described.
But, all this is speculation. At a fundamental level your question, "are they aliens?" is unanswerable.