The textbook you quoted is that of high school and probably written by high school/college teachers. Most of these side notes are often traditional hearsay. As a good scientist of future, do not trust whatever appears in books and Wikipedia should be your last resort to verify historical facts.
Are they all true? If yes, did they have any effect on other scientists whom we know today? And why Indians are then given less or no credit in books and articles?
Sorry to say but most of those ancient "inventions" are bogus. Wikipedia has become a major source of this non-sense. When someone tries to challenge that discovery, it is reverted. The problem with very old historical stuff is that there is no proof. Suppose a nation A claims today that they invented sines and cosines thousands of years ago. What is the proof? Is there any surviving manuscript? You see the problem with very old historical stuff including the origins of a certain concepts and giving due credit where it is due is one of the most difficult questions in history. Human history is often dependent on the author. You have to be critical when you read a rosy picture of any civilization.
Recently, there are series of rather ridiculous claims in History of Science and Mathematics, and even Physics that everything originated in ancient India. Claims range from invention of alegbraic formulae, sine, cosine, numbers, astronomy, distance between Earth and Sun, ancient air crafts, stem cell research and above all close relationship of German and Sanskrit. Usually Wikipedia and other dubious sources are quoted. BBC even made a report on it, sadly this is being propagated by some obscure university professors.
However the easy question is what is the contribution of modern Indian scientists?
Some Indian scientists during the time of British made really major discoveries while working in India such as Sir Chandrashekhara Venkata Raman (Raman effect), Bose (physicist), Meghnad Saha (Ionization equation), Ramanujan and many others. Yes they faced difficulties in publishing in major journals and even faced inappropriate comments. However, later on they earned the respect from a majority of the scientists in the world.
An example is that of the interview of Arthur Compton's wife. She recalled her encounter with Raman as Ref: C. V. Raman and the Discovery of the Raman Effect, Phys. perspect. 4 (2002) 399–420,
" In an interview in 1968, although she could not at first remember Raman’s name, she stated: Anyway he [Raman] was very dark, just as black as could be, but he had a beautiful Scotch accent. He would be asking questions from the back of the hall, and it was so disconcerting to have this person, black as coal, with this beautiful Scotch accent. He was the one who said, ‘‘Compton, you answer questions well; you’re a good debater, but the truth isn’t in you.*’’
Today such labels would not be acceptable such as "black as coal" in any community.