This looks correct to me. Logstash has normalized your timestamp to UTC and will show the timestamp according to the user's browser's timezone. See: How to set @timestamp timezone?
Example:
Original: 2024-01-23T23:14:14.004318+05:30
UTC Time: 2024-01-23T17:44:14.004Z
Which matches what you're seeing.
Though it does look like we're saving these values to timestamp and not @timestamp you might want to change your date filter to:
date {
locale => "en"
match => [ "timestamp","ISO8601"]
target => "@timestamp"
}
Otherwise my guess is that you've got a timestamp field and a @timestamp field.