If your takeaway from your link was that "it's fine" and not "that further research is necessary"... you are going one step further than the article.
I can understand why people don't want screen time when their kids are toddlers -- you only get to raise your kids once. If the jury is out on whether or not "screentime" is bad, some parents err on the side of caution. Regardless, kids are malleable enough that any "familiarity gap" that the "iPhone user from age 2" has over the "iPhone user from age 6" has will likely be near zero within a few months at that age.
What benefits have you found your child to have derived from relatively early smartphone use beyond being able to have access to their parents at any time during the day?
My personal take is that, as with all things, moderation is key.