No, but newspapers also served as a clear sign of "I don't want to engage in casual conversation". Really, it's not like before smartphones people were actually talking with each other on the bus. Hell, in the fine era of 1990s, when people stopped reading so many newspapers but didn't have smartphones yet, no one talked with random people either - it's sort of a cultural norm in the west.

I was not alive when newspapers were at their prime. I cannot answer that question definitively, but I will say that it is entirely possible, and does not take away from the analogy. Would you interrupt someone reading a newspaper to talk to them? How about if they were reading a book? Would it be okay to interrupt someone typing or scrolling on their phone to try to start a conversation with them?

Occasionally, but because the newspaper was large enough to present a physical barrier between you and the person you were talking to -- large enough to hide your face! -- you didn't do it unless you wanted to send a very clear message that "this conversation is over."

Why would people choose to speak to strangers when they can communicate electronically with their friends 24/7? The fact is that whether you're introverted or extroverted, phones now suit all your needs as both a device to keep you occupied and as a means of communication.