I think what he means by 'historical decline' is that in centuries past the vast majority of people were either farmers or what would be considered small business owners. Only around the time of the industrial revolution did there start to be mass employers in the private sector.

Also it's probably a bit misleading to throw out the 244% statistic without giving the overall relation of self-employment to regular employment.

"In relative terms, the share of self-employed within the labor force grew from 14% in 1969 to 21% in 2006 in metropolitan counties, and from 11% to 19% in non-metropolitan counties."

So while there has been a 244% growth, the self-employed still make up around 1/5 of the total work force. Historically I'd assume more than 60-80% of the work force would have been considered self-employed. Ignoring certain circumstances such as slavery, the only historical mass employers would likely be governments/military. Perhaps in times of war a large portion of the work force would be conscripted into military service, but most of the time the majority of the population would be farmers or local tradesmen.