Ditto copies the catch rate and typing, so I think it was just a coincidence. I can't prove it, though.In gen 4, when catching dittos, if Ditto transformed into a water or bug pokemon, a net ball was effective at catching it.
I just tried this little trick and I'm not sure it works that way anymore (considering the lvl 63 ditto that had transformed into a golduck broke out of the net ball immediately twice, when an ultra ball caught it first try. It was in red health, no status).
Can anyone else verify this?
Also, I don't think any stat changes done before he transforms apply to Ditto after he transforms. Though he'll probably only be used with his DW ability, still not bad to know.