Apple and IBM have had a partnership as far back as 2014: https://www.apple.com/newsroom/2014/07/15Apple-and-IBM-Forge...
I remember as part of that partnership IBM released a version of their MobileFirst tooling that was identical to a previous version except it had Android support removed.
Tim Cook was with IBM for 12 years before Apple.
Outside of that, IBM/Watson seems like a comparatively bad choice of partners.