I don’t quite understand your confusion - did you read his comment as “at any point since its founding [i.e. just not before 1776]”?
“Since it’s founding the US has never been a welfare state in any sense. Change my mind!”
> If one must keep that in mind, may one ask what definition of "welfare state" has applied to the USA since its founding?
The contention was definitely whether it has been a welfare state ever since its founding. No judgement though - the English language is terribly poorly designed, so I can totally understand how you read it that way.