It doesn't mean anything though. If MK Dons were playing Spurs they'd get a massive gate and then be back to 6K for the next league game. We're not them. We didn't have a great start last season, and especially the year before, but it didn't effect league gates. It won't this time either. Nothing to worry about. It's just one game where the enthusiasm hasn't met some people's expectations. No big deal. I know a lot of people who have binned it off because of the price. No point over thinking it, and it will still be decent and it'll be very noisy regardless.
When Ipswich played a PL side at the same stage last season the gate was 10,000 below their league gates. It was £20 for adults and £8 for kids. How many would they have got at £38/£26? It's the league cup early stages, it ain't that big of a pull.