God's existence cannot be demonstrated or proven, and so that puts the concept of "sin" in the same boat. You can't very well act against the will of a God that doesn't even exist in the first place.
As an aside, the article's author was a bit all over the place... like the way she mentioned her interaction with the little boy and the parents' harsh reaction to it, went on to complain about the hospital staff for a couple paragraphs, and then came back to the little boy and his parents as the example of racist sinners in action. She took a break from the main point of her entire "article" (if you can call it this - it is quite a mess) to air her grievances with hospital staff. This is stream-of-consciousness type writing, which could be okay in some contexts... but that is definitely not what this particular author was going for, I can tell. With her claims of "doing her research" (let's hope she doesn't write about it) at home under quarantine, etc. Her ideas are out there somewhere... without a hope of them coming down here to Earth, unfortunately.