> I do not understand why hot_updates value is not 0 for pg_database? Given that reloptions is empty for this table that means it has a default value of 100%
Maybe I didn't entirely understand your question, but why would you assume they are somehow related?
According to the documentation [1][2]:
pg_class.reloptions: Access-method-specific options, as “keyword=value” strings
pg_stat_all_tables.n_tup_hot_upd: Number of rows HOT updated. These are updates where no successor versions are required in indexes.
The value of n_tup_hot_upd is not zero because there are tuples that were HOT-updated. That's it. You can read more about HOT here [3].