I think that if you create a new project (it creates with Name, Begin date and End date columns visible) and import CSV in expected format then it will work fine. If it doesn't please share your CSV file.
PS. I really do not understand this:
even when I upload the "HouseBuildingSample.csv" from the site?
What site (there are many our there)? Who created that CSV (we do not ship any CSV files with GanttProject) Why upload from (usually you upload to and download from)?
But hope that it just doesn't matter. If it does, please try making it a little bit more clear.