No, it will have been cached by Google.
So, rather than checking Wikipedia every single time someone searches for "Mumsnet", google will check Wikipedia the first time, and then store that data for a while on their own servers, so that it doesn't have to query wikipedia every single time anyone searches it. When google decides that data is too old, then it'll check Wikipedia again, but that might be once a month for instance.
The alternative would be for Google to ask Wikipedia for the relevant info every time anyone did a search for anything with a Wikipedia article, which would likely be enough traffic to bring Wikipedia down.
Basically, imagine you've got 5 kids who keep asking when dinners going to be ready. To stop them interrupting you, you chuck a sign on the kitchen door saying "Dinners ready at 5pm" and change it every 5 minutes if the situation changes. However, at 4:45pm you get a phone call, so push dinner back to 5:30pm. At 4:48pm however, you've not got round to changing the sign, so while you know dinner is at 530pm, if your kids check the sign they'll still be expecting it at 5.
(Guess what I'm getting nagged about at the moment!)