On its return they found organisms that were too large to have originated from Earth.

Too large? They had two choices -- too large and too small.

To be "too large", the organism would have had to be larger than an ostrich egg yolk, the single-cell record-holder for size.

To be "too small", the cells would have to be very small indeed -- the smallest earthly cells are extremely small.

In any case, if the cell has DNA, it's from here, so first run the test, find the DNA, then don't publish this ridiculous claim.

"Extraordinary claims require extraordinary evidence." -- Carl Sagan