Caching. That number is expensive to calculate so it is heavily cached. It will update sooner or later.
It is also not customized per user and shows the total number of reviews in the system, including ones that may be no longer available to you.
That orange notification shows everyone the same number, which is the total amount of reviews. That's why when you reviewed, the numbers didn't match up. If you are the final reviewer on a certain item, the total number will drop by one. The notification does not show when there are less than 2 total reviews.
Also see Notification for reviews shows way too ...
The user, "fred", wrote a new answer. That's why the question was bumped to the top of the list.
It turns out the new answer was just a rant, and didn't answer the question. Three users with sufficient rep, in this case Charlie, imsodin, and myself, apparently flagged it as "not a answer" (or maybe voted to delete it, I don't remember). When enough users ...
It looks like SE deleted an account network-wide and all the votes that went with it. Lots and lots of users lost rep last night someone on gardening losing over 2000. If anybody remembers how lots of old questions were getting upvoted, well it was that user.
In total on this site, it was just over 1,000 upvotes plus 8 downvotes.
Massive user ...
I couldn't find where I read it but there are two things that could be going on here:
The counter displays the total number of tasks that are available for review. This may also include such that you cannot do for some reason. Think of questions to close where you already have voted but there are still votes needed to get a close decision or reviews that ...
Basically, Fred with a reputation of 1 posted a now deleted answer and it shows up as last modified by Fred. Not always, but given the new users rarely ever bother to edit their posts and a rep of 1 is usually a sign of spam or low quality, its a really good guess.
You need 2000 rep to see deleted posts.
I'm not trying to say you didn't get the results you got, or that you're wasting anyone's time. I just don't know what search terms you used to get your mayonnaise result.
I tried cougars and got 22 mayonnaise free results.
I tried precautions and I got 91 results. I scanned the first 50 and didn't see mayonnaise.
I tried cougar precautions and I got 1 ...
There is a meta.se post on this that explains it. Basically any time you have hit skip on a review item, that item still counts but you do not see it.
If you go into your full review items you can see which ones you have skipped.