If you'd like to leave out the table's caption, you can't simply leave the braces empty but must write <tt>none</tt>!
This mode is based on Michael Wichura's TaBlE package for PlainTeX. The official manual for it is commercial (about 40 USD), see http://www.pctex.com-- but note that the TaBlE manual only talks about the original syntax, which does not use \NC, \HL cum suis.
The only ConTeXt docs about it are in [http://www.pragma-ade.com/general/manuals/ms-cb-en.pdf ms-cb-en.pdf].