Smart Weed Problem
This has been a banner year for smartweed. Last year was also.
The weather has been so ideal that its seeds in the soil (called a soil bank) has continued to sprout all summer and up until recently has been putting out new flushes of seedlings. Dryer years this doesn't happen.
Keep pulling. It will be worthwhile because you'll keep seed population down. Here's more: https://extension.umd.edu/hgic/topics/smartweed
Of course, you may want to mulch more next year, too.
pulling seems mission impossible; have 500 square feet and stuff is big and thick
I've heard that one solution is to cut it down to the ground and use a flame thrower on the dirt to kill seeds
ever hear of that?
You could do that. You could also mow on the lowest mower setting.
Could also cut/mow, then rototill it all under to decompose over the winter.
It works well to cut, then cover an area with 3-4 layers of newspaper, then mulch heavily, though your area sounds rather big for that.