It has some of SE20 in it too (the bit where I live, mostly Edwardian and interwar terraces). Labour and Lib Dems were active, didn't hear much from the Tories who I got the impression had given up - their incumbent councillor was retiring which might not have helped.
I don't know Grove Park that well but I guess the Lewisham Tories put most of their effort in there whereas in Bromley the line of defence was perceived to be further back.
In terms of demographics, the bit I live in has a lot of young families and anecdotally there has been a lot of overspill from Lambeth, Lewisham, Southwark etc as people move out for more space. So the demographic change has been more London than Kentish. Obviously a lot of people are taking their voting habits with them. (tbh I'm thinking of myself here!)
I suspect the Tories will lost interest here and future fights will be Lab-LD.