Works for me with GDAL 3.1.0dev
ogr2ogr -f "ESRI Shapefile" negative.shp negative.json
Warning 6: Field sweepTime create as date field, though DateTime requested.
ogrinfo negative.shp -al
INFO: Open of `negative.shp'
using driver `ESRI Shapefile' successful.
Layer name: negative
If a spatial index for a Shapefile was created by GDAL, you will have a .qix file side-by-side to the rest of the Shapefile's files. And yes, the process is usually very fast.
If you want to see more output and have GDAL tell you about what it is doing, you can enable debug messages using --config CPL_DEBUG ON. Here is an example:
$ ls -1sh file.*