I'm a data point that favors surrounding noise. For years, my most productivity-dense time of the week is when i bring my laptop to a local sports bar for prime time NFL games. Something about the consistent noise, available momentary distractions and wandering eyes keeps me on-task and cradled in thought in a way no office (home or formal) does.
I think you've got some cocktail party effect going on there. Conversely, one of the most distracting things for me is barely hearing people talking. My brain keeps trying to interpret the murmuring as words before it can reject it.
Same! My family loves calling each other on speakerphone. Asking however politely and considerately for them to use a headset or hold the phone is a mortal sin.
Coincidentally, when I moved out on my own, my ability to focus suddenly shot through the roof. Like putting on glasses for the first time when you're nearsighted.
Going back home I don't lose that sense of focus. Until the phone calls start again...