I think the answer to this is that sure, automation has replaced some manufacturing jobs however, offshoring/outsourcing plays a big part in the numbers game - even if a company offshores/outsources most of its production process (jobs)to other countries but they still put together the final product here in the USA (they ship back the parts), the Bureau of Labor Statistics counts the entire operation (from start to finish) as manufacturing output.
Bingo...
While that would certainly make things convenient for the people arguing that our manufacturing output is overstated, it has the problem of being completely false. The BLS tabulates output by calculating "real value added." Thus, a part manufactured overseas is not "entirely" added to the total.
Now, people can claim that the BLS output number is inaccurate for any number of reasons, but not the reason you provide.