Reading the S3 plugin https://www.elastic.co/guide/en/logstash/current/plugins-inputs-s3.html#plugins-inputs-s3 there is one line
Each line from each file generates an event. Files ending in
.gz are handled as gzip’ed files.
So, if the file is tgz, or gz, then wil the S3 plugin unzip, and then read each line of the file.