And what alternative possibility explains their data?
I would imagine a protocol of providing the virus particles an opportunity to infect the cells in culture, getting a baseline of the amount of viral sequence in that sample with say PCR, then introducing those cells into a much larger culture, giving the cells time to infect their neighbors, then with something like PCR again determine the level of viral sequence in the new culture to see if replication occurred
but that is me being an armchair-engineer, I am not a scientist so I don't know the limits of their tests
as to how add one thing to another could cause number to go up if not infection - well, that just makes me think of the meat-maggot-fly problem and the simple test by means of keeping flies out that proved the meat did not spontaneously generate life
And what alternative possibility explains their data?
the cells themselves could be reacting to dna sequences like immune cells can, the viruses could be binding to cells and then without infection producing proteins on the surface of cells, the data itself could be faulty, etc. there are litterally an arbitrary number of possibilties
I cannot prove any of these things, it is not my field so I really shouldn't be coming up with alternatives, and it is not my burden to, it is the researcher's burden to disprove the endless possibility of other things and they researchers themselves do not say they proved infection and replication, merely presence of something they believed would increase if their idea was right
I am not opposed to them being right, science is not supposed to be adversarial but skeptical, and you have a jump to conclusions mind incompatible with the process of science