About the create external table
Did you check the correct syntax at the manual? (here)
At datafiles keyword, you don't use the correct syntax. This probably will work.
create external table test_table(cols varchar(10))
using ( datafiles('DISK:C:\sample.txt'), format 'delimited', deluxe);
About the load
It isn't a native command from the engine, is a specific command of dbaccess utility.
So, if you aren't using dbaccess, it will not work.
BTW, the syntax of your load is correct...