Why does MacBook ask for iTunes/iCloud password to open apps?

BACKGROUND:

- I have an iMac and a MacBook.

- On both computers, I use 2 OS X apps (recipe manager app & password manager app).

- I primarily use both apps on a weekly basis on on my MacBook. I don't use my iMac very often.

- For the Thanksgiving holiday, I didn't use my MacBook for a week.

- When I used my MacBook again and attempted to open both apps. Instead of opening immediately, I received an App Store pop-up box for each, saying that the app "was purchased using the App Store on another computer" and that to use the app on my MacBook, I need to "sign in using the Apple ID and password used to purchase it."

- I think (but don't remember) that both apps were originally purchased on my iMac. If so, I then just followed-up and downloaded the apps on my MacBook.

- I don't recall receiving this type of pop-up box asking for my App Store password during previous uses of these apps on my MacBook, including when I fully shut down the MacBook and turn it on again.

QUESTION:

- Is this common protocol for App Store purchases downloaded to computers that weren't used for the original app purchase? Or is this a sign of some type of malware on my MacBook? The pop-up boxes look like legitimate App Store pop-up boxes when you purchase a new app.

Any thoughts would be greatly appreciated.

Thanks!