Yeah, it's pretty intrusive on Microsoft's part with regards to constantly pestering people to install Windows 10. It seems that it isn't the same update un-hiding itself per se, but rather Microsoft issuing another update to supersede the previous update(s) that were hidden by the user.
The first screenshot below was taken from a laptop where the 'Get Windows 10' update initially installed itself, but I hid the actual upgrade update as I don't want it to update to Windows 10. Like you, the update came back and as you can see it's not just one update that I've had to hide, but three different updates for the same thing. Microsoft used to use the same questionable tactic for trying to get people to install Silverlight when users had explicitly chosen to hide the update and not install it.
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The second screenshot is from a desktop where I removed Windows 10 and reverted back to Windows 8.1 with a clean install. After doing so, I went through the big list of updates to hunt down and hide update KB3035583. On this PC, Windows hasn't tried to re-install Windows 10 and all is good. So this is the update that's the key one to prevent Windows 10 trying to install itself.
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However, it maybe worth trying the Reg fix in Brink's tutorial at the following link (Option One, Step 3), instead of just hiding the 'Upgrade to Windows Pro' update:
Upgrade to Windows 10 Update - Enable or Disable in Windows 7 or 8.1 - Windows 10 Forums