She just followed her on Twitter.
She has been a fan of her for years so why follow her now?
Usually with Nicki it means she is collaborating with them (for example, she followed Lady Antebellum and then a song got registered not long after).
Adele is a huge fan of Nicki so it's totally plausible.
Mess at y'all thinking this is a reach (in this case most likely) they've both expressed wanting to work with each other in the past so I don't see why it wouldn't/couldn't happen