The lumps are odd, I can’t think of a product that would come off as lumps like this using a push quern. Unless it is something really odd, like something foamy.

The laumps are pretty amorphous, otherwise I might suggest breaking down something like chestnuts for flour. Even if they were lumps of dried dough or grain balls I would expect them to be more uniform in size?

In Lalibela, Ethiopia, I saw a grindstone that was operated standing — I’d put my certainty at 99%. I’m going to be going back to check up on the grinding to confirm it. A bread is made for Easter. A bread that is made from flour the woman of the house grinds, then makes into bread dough, which she bakes in a leaf-lined terra cotta pot. A lid is placed on the pot and the bread is baked in it with fire under and over. When done and cool a priest comes to the house to bless it. I may have a photograph of the station where the grain was ground. If I can find it — not a certainty — I’ll send it to you.

Perhaps Andrew Dalby would have an opinion about what is being ground.