Maybe she was right, and there were two voices? The female announcement sounds like it was edited. Badly. This might explain the strange verbiage as well ("All buildings" stands out. That particularly phrase, with its inflection, sounds like it originally came from the end of a sentence too). I've heard other people say it sounds like the same voice used by the city during the summer protests or something along those lines.

For the purposes of arguing, let's say someone got ahold of some municipal evacuation recordings and chopped them up for this. It's not likely they had enough phrases to warn people a bomb would be going off in specifically fifteen minutes.

EDIT: For anyone curious about other instances of bad edits, listen to the word "this"; there's another word before that, and it was cut off: "thi-this area must be evacuated now". Also, "if you can hear this message, <unnatural pause> evacuate now." It's not likely any professional voiceover person would announce this way, nor would anyone who's paid attention to basic edits before consider this passable.

If this is all true, I guess the next question to ask is who would have access to those announcements, and who would think to use them? Most people would probably just use some text-to-speech thing unless it was easy/they had good reason. I'm probably overthinking this, though.