This is one of the oddities of flying in the UK.
In every other part of the world that I've ever flown airports operate on the basis that they sort of expect aeroplanes to come and land there. In the UK we have this slightly bizarre concept of "Prior Permission required" and as almost all small airfields are privately owned, it's like any private property, you need permission to use it - and the owner reserves the right to make their own rules.
There is some logic behind it, albeit slightly obtuse. Even though almost all those airfields have been there since pre-WW2, the locals love to complain about noise. So to keep people happy, the airfields agree to limit the movements. By asking pilots to request permission before coming, they can reject requests if they have reached some quota. In some cases the land use as an airfield is predicated on PPR being in operation.
Lesson learned - always call/fill in the online form prior to departure.
Could I have asked more questions or tried to get in anyway?
You can always ask, but their land, their rules. It doesn't matter if there was 1 or 100,000 movements that day. Busy or not, it's their choice. Of course, as an uncontrolled airfield they cannot give you permission to land or otherwise. Don't expect a warm welcome if you land there against their wishes.