Reason he said that is he knows well enough how thick a standard 010 block is. A standard bore going to .030-.040 is safe as the thickness in the block as produced was sufficient back then to provide material for an overbore without any guess work involved.Older blocks tend to be heavier or "overbuilt" as you might say.
With a block thats allready bored, its best to know if it is thick enough to take another overbore, for the horsepower rating it will be built to, and for the material to be sufficient for heat transfer/absorption so to promote good cooling.
Newer blocks are lighter and have less material due to that, so sonic testing is a good idea to ensure no problems will arise.
Fact is stranger than Fiction