They do not equate to it, but they can cause it. In the example the OP was giving the phone would have been compromised by a side-loaded app. Quite possible.

Every android phone I've owned has required me to check a box hidden in the settings before I could install from outwith the Play store. My current phone gives me an additional pop-up warning that this is a security risk which I have to agree to before it will enable side-loading.

Ultimately you can't completely protect users from their own stupidity. You have to make the security vs usability tradeoff somewhere. I appreciate that my phone allows me to manually install applications - it is in fact one of the reasons I chose it.

Yes because clearly no major company would want to spy on you through its official app...