in short - when your computer asked for "dffd.wimbli.com" your ISP said "lol who is that?" when they should have forwarded that question onto other DNS servers until they found an "authoritative answer". since they didn't, your computer was under the impression that dffd didn't exist on the internet anymore, giving you those errors.
by changing them from whatever they were to 8.8.8.8 and 4.4.4.4 (although as jthill pointed out, 8.8.4.4 is a better secondary), you stopped asking your ISP where things are and started asking Google.
This is a fairly decent explanation... but one thing you should be aware of is that this can be a sign of other weirdness from your ISP.
Properly functioning hierarchical DNS (Domain Name System) is a cornerstone of the Internet; if your ISP is bad at it, whether due to incompetence or malice, that's something you should be a bit concerned about.
Some things I've seen:
* If your ISP has been bought out at some point, they may have changed their DNS servers but not properly pushed out the changes to end users. It's also possible that they made changes on their end that haven't been picked up by your device; if you've got a DSL modem, cable modem, wifi router, etc. box (most people do) that may need to be rebooted. The "normal" arrangement is that when these boxes boot up they ask their upstream network for info.
* If your ISP is trying to cheap out by using a caching system, they may be playing games with returning things not found at first if they're not cached at your ISP, and trying to then load them later. Sometimes this results in "doesn't exist" messages for a website at first, then if tried somewhat later (minutes to tens of minutes, usually) it will work. Normal caching shouldn't do this, but if you turn the "be super cheap at the cost of user experience" parameters way up you can see this. The only legit reason for this sort of thing is if you're getting to the Internet over a *very* slow connection, like satellite or an old microwave tower.
* More worrisomely, you can also get this sort of result if your ISP has implemented various sorts of more-or-less-evil redirects to monitor traffic or serve you additional ads.
* It's also possible that malware on your computer was redirecting your traffic, although that's less likely if you hadn't noticed other problems.
As a side note, switching to 8.8.8.8 (etc.,
Google Public DNS) means that Google knows about every website you visit; simplified, every time you type in an address, it checks with Google to see how to find it. For many people, this isn't telling Google anything they don't know already, but just FYI. (Normally, that info would be handled by your ISP; which can still see the traffic going past even if you're using Google of course.) If you're someplace out of North America, there's a chance that it may slow things down compared to a local DNS provider; of course, the OP started this because their local one wasn't working.