Doesn't sound very likely. You can book your interview for whatever date/location that is available so would make no sense in holding back results as you could just book an interview somewhere else.
I think what is more likely is that NATS are 'erratic' in their response times. It (probably) bodes well that somebody on your day has been refused and you haven't heard yet.
It can be frustrating but if you're really worried then call HR and ask.