I suspect TPL has moved because its Mcap is far smaller than CUL's. CUL has other interests such as Fe in Pibara and a string of other non Coal tenements around. I expect the market has discovered TPL is undervalued for the land it holds. Compare to QLD companies in coal in surat Basin for example.
Ps: Also check OBL's recent rises, it also has a smaller M.Cap than Cul.