It’s not a live counter, it’s only sampled occasionally. It’s not strictly caching, but the counter is never completely up to date.
The counter is supposed to be updated every 8 hours, but sometimes it can take longer. It’s also possible that your deletions just may be having less of an effect on your usage than you would have hoped.
Do you know how many files and directories you’re supposed to have? And what does the counter say?