Based on what? Didn't fidelity post some scientific evidence saying that the chances of this being man made were quite small?
That's what I posted in the mega thread. There are changes in the virus that we wouldn't have envisioned or designed based on our understanding of biology, but evolution has pointed out to us. So unlikely that this virus was stitched together. Most likely an isolate, like the 99% identical one in pangolins, jumped into another species that has a humanlike ACE2 receptor and got better (through selection and mutation) in using it. Could have been in humans too and in one person, after a bit of replication, a fortuitous for the virus unfortuitous for us change occurred.That's what I thought also, something about markers that should be present if it's man made or been tinkered with but they're not.
While not genetically engineered, there is also a chance that researchers took a pangolin like isolate, passed this CoV on human cells for an extended time, and "evolved" it in culture. Can't rule out this possibility based on what we currently know.