Why did my contacts appear on my girlfriends Viber?

[Windows Central Question]

So my girlfriend randomly received a message from my friend in a group containing 24 people. The problem is that almost all of those contacts are mine, and only few of them are hers.
It consists of random people from my phone contacts, some are my friends and colleagues and some my acquaintances but I am not inside that group. I have never formed that group on my phone or desktop app.
I am pretty sure that most of these people don't know each other and I know that some of them only I know (like people from work), so these contacts must be mine (someone else couldn't have formed this group with all of them in it). The problem is how did that group form (there is no admin) and how did these contacts end up in her phone.
Some of them are named differently than in my phone (like without a surname or without a nickname I use for them) which only suggests that she didn't have these contacts saved in her phone memory and the contacts are shown as Viber names people chose to share.
My friend (and hers too) who sent her the message containing a link to a video doesn't know almost any of the people that are in that group. None of the other group participants commented or shared anything.
If it helps in any way (doubt it) she has a Windows phone and a desktop app and I have an Android phone and a desktop app.
Some help or suggestions would really help to reinstate the trust (at least) with this app...
Thanks in advance!

 

[humzahyaz]

Do either of you have the same account synced with your devices?

 

[kopiledon]

Each of us have their own account and a mobile and a desktop app (they are synced). I hope that this is what you asked me cause I did not quite understand the question...
I just got on the phone with the friend that sent her the message and he said that this group he just found on his Viber app and thought that it was another group he usually uses so he just sent the message there and wasn't aware that it contained people he did not know until I asked him about it. Usually Viber notifies you that someone added you to a group, neither my friend or my girlfriend had this notification.