Wrong update date in the AppStore lists
Not to take away from Allan's or drivec's answers, as I do think they have pieces of the puzzle, but the real answer is a little more complicated. 

drivec is correct about a 'bug', but the bug is actually an interaction issue between iOS 11 and the iOS App Store. 

This bug presents itself by listing apps as having fresh updates, when many of them do not!

Example

I have an iPhone 6s, as does my wife. I also have a number of apps I've developed, available on the App Store. As you would imagine, I have these apps installed on my iPhone, as does my wife. 

Now, here are the interesting things: 


During the last couple of weeks, in the Updates tab within the App Store app on my iPhone, I've seen a number of my apps listed at various stages. Now, these apps have not been updated since Feb/Mar/Apr of this year!!! 
My wife's iPhone does not list these apps as having updates available, even though the same apps are installed on her phone. So, I got update notifications for apps I know have not been updated, and my wife hasn't received the same notifications.


The first time this happened I was rather confused, to say the least. I looked at my apps on the App Store and they still showed me as the developer, and they still showed the correct version numbers and in the Version History the correct timeframe of when the latest version was released. But, if I go back to the Updates screen, it'll show 2 days ago, or a date from last week, etc. 

I reported this to Apple and they are aware of it (having received reports from other developers). And it is something they're working on.

Finally, Allan is also correct because the dates shown on the Updates page does indicate the date the updates were installed, while going into the App's individual pages and looking at the version history shows the date the app's latest version was released. 

However, because of this bug, what is happening is that people are installing updates when in fact there is no need to do so, but when they do the dates appearing on the Updates tab change to the more recent date, even though the exact same version of the app may have been released months or even years earlier. And, since this bug is not necessarily presenting itself on all iPhones, or even with the same apps on different iPhones, it's only adding to the confusion.

NOTE:

When speaking with Apple about this, they informed me that they were updating apps so that they're signed with Apple's latest signing certificate. However, in those cases, Apple was pre-populatng the "What's new" text with the following text:


  This update is signed with Apple's latest signing certificate. No new
  features are included.


So, if apps are listed as having updates available, and the above text is shown, then they're not being affected by the bug I refer to here in my answer. However, it is possible that perhaps they're appearing in the Updates tab because of the certificate signing, and for some reason the "What's new" text isn't pre-populating correctly.