You can certainly use an ETL tool to populate something that isn't a data warehouse - for example I'm currently working on a process that de-duplicates data and populates a CRM system. I'd call it an ETL process. Looks like a duck, quacks like a duck.
However in the case of the question that the OP is referring to, the task the poster seems to be trying to achieve might be better described as data-migration than etl.
I'd say etl belongs on processing with significant 'E' and 'T' (extraction and transformation) components. ETL is traditionally associated with data warehousing and the term was coined in that context. However, populating data warehouse systems is a long way from being he only application for ETL processes.