You can't invade solo host unless they specifically use an item for it
If you are coop you open yourself up for invasions and since a session has a 4 player limit you're always either in the majority (aka ganking) or on even grounds if you decide to only summon 1 friend and let the invader live long enough for another to show up. If you invade you are pretty much always going to be in a 1v3 situation.
In the game, there are stones that you can find, and when you use them, they say something. There's no voice chat in the games, so these can be used to communicate
Your character doesn't speak per say, so you usually are limited to gestures for interacting with other players.
The stone refers to a series of items thatve been around since dark souls 1 where you drop a magic stone and a voice comes out saying the line. In dark souls 1 and some others it was a rock you dropped and it broke open making sound, so the "stone" term stuck.
In elden ring it's called a "prattling pate: 'voice line here'". Your character blows into it like a flute kinda and the line is spoken.
Basically the guy showed up, said "damn ur fashion is on point" then left :)
I've played rescue ranger a couple of times, legit one incident I intervened in was some poor bastard running for their life across the entirety of Liurnia Lake while the invader was leading an angry mob of enemies chasing them
Night and Flame got a workout that day, lemme tell y'all.
I don't really engage with the online mechanics in Elden Ring... Maybe I should? I've put hundreds of hours into the game otherwise. I rate and leave messages but I've never summoned help for co-op or invaded people except for Varre's quest where I always just get obliterated by people who are way better prepared than me.
Not quite the same, but in WoW, you couldn't talk to the opposing faction. So sometimes people would make characters like this just to hang out in the other faction's zones and communicate using only emotes. Good times...