The webpage has a typo and is missing a leading '1'. The Nyasa-Vidya is described in the concluding 6 sections of the Taittiriya-Narayana-valli aka Mahanarayana-Upanishad. This would make it sections 149-152, not 49-52. The numbering also is broken. Rangaramanuja's version of the Upanishad has only 150 sections and Nyasavidya is covered in sections 145-150.
First of all neo Hindus like Arya samajis who do not believe in traditional dates, and tradition that vyasa edited the Vedas claim such stupidities all the time.
Anyway they claim many things to be interpolation which doesn't subscribe to their philosophy, it was dayanand who first said that Veda is only samhita, many neo Vedics have followed in his path. ...
MadhvAchArya did not write a commentary on the Mahanarayana upanishad.
The following are the works of Madhva as given by B N K Sharma in his work A History of the Dvaita School of Vedānta and Its Literature.
There is no mention of any commentary on Mahanarayana upanishad by Madhva.