Hmm indeed, the output is very weird. When you open the file with a text editor can you read it? It seems that you are dropping the existing database to create a new one. If you used Delete invoice, table of accounts etc - #24 by dave I think you have to make a new sql dump. You can use point 3 for that, but for the second command just use:
$ sudo docker exec tryton-postgres pg_dump > <your backupname>.sql
Using the -c -C adds some extra data into your dump which you don’t need. You can also edit your existing dump and remove any lines which says something about dropping or creating databases and users. This lines are probably at the top of the file. 
If you are going to modify your sql dump, make sure you have a backup!