Are all seeds from fruit?

sort of depends on what definitions of "fruit" and "seed" you are using, because in some ways of interpreting the word, the idea of seed is also a fruit for many plants.  this would be the case of wheat grains (grass seeds as others have claimed as being not fruit are, botanically, fruits) because a fruit is a non-reproducing part of the seed body that forms from the ovaries of the parent plant and encases the germ cells that are the "seed".  Many plants are not flowering plants and produce no fruits in the biological sense, yet they can and do produce seeds in that same sense of germ cells.

Lots of plants produce seeds without having an edible fruit, or even a fleshy fruit, though.

No. Some seeds come from vegetables. Though all plants (including vegetables) have fruiting bodies. 

When you use the word 'all', the answer is typically no as you just need 1 example to disprove it.

Grasses have seeds yet not a fruit, so nope.

Nope. Bird seed comes from grasses like millet. 

Weed has seeds. Is that a fruit?