The picture you posted shows two plants; one with trailing stems, and one floating on the left with a few bits sitting on the left section of wood. The trailing plant is not Lemna minor. L. minor does not grow leaves on stems; it consists of a thallus (a plant body not differentiated into leaf and stem) with a single root. The small floating plant does look like some kind of Duckweed, quite possibly L. minor. You will find, if you pull the bits off the wood, that it is not really attached but just stranded - Duckweeds cannot attach themselves to anything.
I have found that Thin Duckweed (Landoltia punctata) can survive indefinitely when trapped underwater, but it does not reproduce in this situation.