Isn’t it more accurate to say that they are both based on Resque?
Sidekiq credits BackgrounDRb and Delayed::Job and Resque as inspiration here: https://www.mikeperham.com/2022/01/17/happy-10th-birthday-si...
The API is very close, but architecturally it's different.
Additionally, delayed_job came before resque.
Resque was the main inspiration, Sidekiq still provides compatibility with some of its APIs to this day.
https://github.com/sidekiq/sidekiq/blob/ba8b8fc8d81ac8f57a55...