That theory is not compatible with how you can trace variants of the spike protein and its evolution and also trace it back begore the pandemic to the lab and decades of research by DoD, Wuhan Institute of Virology and EcoHealth Alliance, ralph Baric, Peter Daszak, the US patents. The PRRA insert and furin cleavage site, The HIV GP120 insert, not found in any naturally occurring coronavirus. But i get why the culprits behind the engineering of this virus would love for the theory that there exist no virus to spread.
Discussion
The idea that some random particle from the unfiltered BALF "soup" is pathogenic *IS* the theory until properly proven otherwise. On the other hand, what I described is not theory, but a highly questionable process documented in the scientific paper claiming to have found "new coronavirus".
It is very compatible with other previous virology research in a sense that all of it is based on bad practices, where they extract RNA from random cell debris and then computer generate the sequences using special software. In that particular paper that you mentioned, they did not even try to prove pathogenicity, but in others they kill starved cells injecting them with BALF "soup" along with antibiotics and without performing any control experiments claim that it was the virus that killed them. Which is utterly unscientific.