@timestamp and timestamp...difference

Dear Community,
I feel bad asking questions here again and again but I cannot seem to find the answer. I would be extremely grateful if you could help me.

When I explore Robot Execution Logs on Kibana, I find 2 fields for timestamp.
@timestamp and timestamp

I see that time value is identical for each field.

Can anyone please explain to me the difference?

*I find this page, which says that @timestamp is added by Logstash…but I do not use Logstash…