Is scientific understanding based on predictive power?

[ryokan]

So it seems from your response that 'being scientific' is a collective thing, possibly even (gasp!) a cultural thing (even a 'culturgen' or a 'meme'). It also seems that 'being scientific' isn't binary ... it can develop gradually, be partly scientific, etc.

No.
There are medical problems or physical problems which can be understanded by scientific or non-scientific (mythic, for example) forms.
It cannot be said that a community or an individual was ever (or never) scientific. I believe that Kepler made astrological predictions. Nevertheless, his laws about planetary orbits were very important in Science.
The 19th Medicine was plagued with a lot of non-scientific beliefs, any of them remain in our century (homeopathy).
Nevertheless, there was important scientific advances in Microbiology, cellular theory and so on. That is out of discussion.

BTW, when was the work done - in London? - that lead to the discovery of how collera (?) spread (infected wells?)? Wasn't that 19th C (or maybe 18th)? IIRC, the method used was almost textbook scientific!

Yes Dr. Snow, 1854, London. I have found very interesting this link: http://www.ph.ucla.edu/epi/snow.html