I don’t have Snapchat so quick question. Would someone you’ve never talked to be in your messages with no actual conversation? If that makes any sense. It was two different people that the person isn’t friends with on Snapchat from a couple months ago
If both ends added yes but either deleted convo or no one spoke
When you add a new person it instantly creates a convo matter of fact it encourages you to send a message. Like say hello to your friend something like that. So even if they never send a message it will be a convo unless the convo is deleted
If both people added each other, then yes that username appears on the recent chats screen. This occurs regardless if you ever sent each other a message.
But, chats also auto delete if you don’t have it set to save a chat. So, there’s a possibility chat history could have been going, but it doesn’t show.
OMG, I’m here for the comments because I don’t understand Snapchat. 
Snapchat wouldn’t show pictures or messages unless you set it to not delete. Messages disappear after you look at them on Snapchat.
If you add someone it wil show up in the chat. But if you don’t message it will say something like “send a chat” but if they messaged each other, it would say sent or received
This sounds more like “is my significant other talking to someone else” and the answer is it doesn’t matter you already don’t trust them
They probably have friends in common so yes they show up and so long as it says tap to chat no messages have been sent.
When adding someone their name goes to the chat but it will be an empty chat. If you are not friends they will not come in your chat side unless there has been msgs sent - msgs either disappear when you back out the conversation or within 24 hours and there is no way to get a msg back on Snapchat.
Snap also tells you and the other person when you screenshot
if they’ve ever said anything. or responded to a story yes
These are typical things of what it might say next to someone’s name. If it says tap to chat it means you’ve never talked to them before. All the other things have some type of communication going on. But you can also be friends with people on there and can delete the conversation off of here by holding down over the person and going through the options - one of the options says clear from chat feed. Then you just have to go find them in your friends list to text them again.
I’m gonna say yes. A few months ago I got it after not having it for years and there were a few people on the chat list I have never even heard of.
I’m guessing you are looking thru your SO phone. If you don’t trust that person why are you with them?
Snapchat automatically deletes messages so all the people will not have messages. If you see messages Snapchat is glitching and could be a partial amount of messages or in no particular order.