Default-ttl is set to 0 by default if it not harcoded in the config file. Which means that records are set to not expire unless overwritten by the application.
Its not really a problem, but more of how aerospike handles deletes to ensure high performance. For more details please read Deletes More info…
In your particular case you should be able to use Method#4 to clean old data and ensure that your test sets does not return. Please see: https://discuss.aerospike.com/t/bin-names-deletion/731
You can also use Method#1 by setting a default-ttl > 0 and wait for that data to expire prior to restarting the node. This method assumes that record was not initially set to a default-ttl of 0.