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.
Side-loading and non-jailbroken are the defaults. Google is warning everyone to only download from the Play Store but few pay attention and everyone wants something for free.
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.