See: Instructions to Enumerators, 1930 Census:
https://www.census.gov/history/www/through_the_decades/census_instructions/1930_instructions.html


As for places of birth:  Paras 167-169 instruct the enumerator to list the country as it is today (1930) Not the country it was at the time of birth.  Make sure. for example,  that the answer "Russia" is not Estonia or Lithuania today.    It appears that the response to this follow up question was "Kiev" so  Russia is correct, and no addition or correction was required but he wrote the answer he received  anyway.

As for the three letters "M":  The letters he over-wrote are faint on the page  which I found on Ancestry.  I think his fountain pen was running out of ink. The first ball point pens appeared in 1947.

This page of the census is not the only one with corrections or additions.  Almost all are in the same handwriting as the original entries and it appears that he, himself did this as he went along.  The only exception seems to be on sheet 2, lines 13 - 17 where the correction has an initial letter that does not match.
As for the answers being correct or incorrect- The enumerator can only write what he hears.

 David Rosen
Boston, MA