It looks NBD has pulled out of the bidding for IDBI. That would explain their decision to buy a stake in RBL
https://www.retailbankerinternational.com/news/emirates-nbd-to-quit-idbi-deal/
Emirates NBD has decided to quit the proposed acquisition of IDBI Bank and is expected to seek a majority stake in RBL Bank, reported The Hindu Businessline, citing sources.
The Dubai-based financial institution offered $6bn to $7bn for a 61% stake in IDBI Bank in May this year, after talks with the Department of Investment and Public Asset Management (DIPAM).
However, Emirates NBD is shifting its focus to RBL Bank, due to delays in the completion of the IDBI bank deal, said the publication.