The "closest constituency" thing often seems to do what's geographically closest. I also "got" St. Ives, but that's presumably because St. Ives is the closest constituency to Maryland. The heatmap showed that St. Ives was only middlingly close to me politically, and the constituencies I noted looked reddest on the map (although there was no way to look at the "best" one that I saw).
Yeah that definitely has to be it because I got 98% Labour on my test (followed by Greens, Lib Dems & SNP on 94, 93 and 91 respectively) and somehow ended up with Great Yarmouth as my "closest constituency".
