It is quite impressive. I have not yet understood how it works. It seems not to work on the following dictionary:
where one solution is eehnortw covering four words but your script says  aceesttx : exactest.
Update: After further study it looks to me, that you are checking all 8 letter classes derived from the 8 letter words in the dictionary and see how many words are captured. Which is probably giving you the correct solution for many real world dictionaries. This way, you do avoid the combinatorial explosion that makes this challenge difficult...
Still quite impressive!