You're completely correct, search results are cached.
This was easily verifiable when they released tickets while I was searching for tickets a few days ago. If I searched "Olympic Park venues" & "All days" I got very different results compared to search "Olympic Park venues" & "28th July -> 12th August". Clearly those two searches should always return the same result set.
I suspect the website uses a materialised view that only refreshes every hour or so.