I suspect the pop up was designed to make me buy LR6 but I only bought LR5 in the last 6 months; Adobe support have sent me a link to let me upgrade from 5.7 to 5.7.1 (which may be as far as I can go)
The answer to your first subject header question is "no." Adobe misworded the pop-up. If they wanted a pop-up notification on standalone LR5, it should have said, "Upgrade to LR6 now available," with a link, because it's not a free update, it's a paid upgrade. Instead they worded it in a confusing fashion, yet another effort to try and get you to subscribe to Creative Cloud. If you want HDR or panorama merge, and don't want a CC subscription, you have to buy LR6 upgrade for $79.99.