A proper name refers to an identifiable entity, so it is definite. But الرَّجُلُ is definite through the article, not because it is somebody’s name.
Likewise, هَذَا is a definite demonstrative, not a proper name.
Therefore definiteness and proper-name status must not be confused.
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Definiteness and Proper-Name Status in Diptote Rules
A proper name refers to an identifiable entity, so it is definite. But الرَّجُلُ is definite through the article, not because it is somebody’s name.
Likewise, هَذَا is a definite demonstrative, not a proper name.
Therefore definiteness and proper-name status must not be confused.