You could never trust 100% all the apps in the playstore, nothing new here.
Not really, you should first check who is the one that is creating that app.
If the app in playstore is full of malware it means that the one on their servers is also.
Do you think that a mining app that promises 1BTC per hour downloaded from the original website is safe?
Besides, a lot of trusted apps I've used for years can't be downloaded from their official site and link to the store.
Also, if you don't trust play store, how do you manage your updates for the apps? You uninstall and install the fresh copy from the original website each time there is an update?
Again, overreacting, most apps are safe as long as you don't go and install apps that make fake claims such as free gift cards, free money, micro earnings and others.
It doesn't hurt to be extra careful but if go full paranoia mode you're better sticking to the old faithful Nokia 3310.
LE:
While doublecking to see if you don't have the habit of only starting topics and then disappear I saw this post of yours:
Eidoo does the same thing I said above, they don't offer a download version they link to the store.
So, how did you managed to install it?