The 1852 LDS edition replaced this with his. Clearly, the people of Ammonihah are not the Lord’s people. The 1920 LDS edition restored the correct this to the LDS text. The same error occurred in the previous chapter—namely, the replacement of this people with his people. For discussion, see under Alma 9:19.
Summary: Maintain the determiner this in Alma 10:20: “well doth he cry unto this people”.