Apple's Round Checkmarks - Where and When are they used?

We are building a cross platform app, and a decisions maker on my team (who is an Apple fanboy) wants all of our "Select to delete" checkboxes to be round, "Like Apple's Mail and Messages apps".

He disgarees that anyone would confuse round circles for radio buttons.

He doesn't care about Apple's HIG about checkboxes, since they don't specifically state that checkboxes should be square Apple's HIG on Checkboxes

He doesn't care that Apple's Sample Code shows square checkboxes, in response, he says "That's not selecting to DELETE an item" Apple's TableViewCell Sample Code

Have all iOS devices always used round checkmarks to delete items, or is this a new change?

Where and when does iOS use round checkmarks?