Doubt on pg_timezone_names and pg_timezone_abbrevs

I used 'IST'  in a query like this -  (timestamp_hour) at time zone 'IST' time_ist and did not get the expected output - timestamp in Indian Standard Time. So I queried the 2 views that provide timezone info and did not really understand the abbrev column. 

select name, abbrev, utc_offset  from pg_timezone_names  where abbrev = 'IST'  ;
     name      | abbrev | utc_offset
---------------+--------+------------
 Eire          | IST    | 01:00:00
 Asia/Kolkata  | IST    | 05:30:00
 Asia/Calcutta | IST    | 05:30:00
 Europe/Dublin | IST    | 01:00:00


select * from pg_timezone_abbrevs where abbrev = 'IST'  ;
 abbrev | utc_offset | is_dst
--------+------------+--------
 IST    | 02:00:00   | f

This is PostgreSQL 13.15 on AWS RDS. We have the same abbrev for 4 timezones in pg_timezone_names.

Regards,

Jayadevan