6 random character prefix automatically added to entire DB tables, how / why?

I’m working on a site, live on server. I’m using Navicat for working with the DB. I have the WP DB opened and am 100% sure the tables were just standard tables, using standard wp_ prefix.

While I’m working on another screen in admin area, I needed some user-meta info, I refresh the already opened DB.. and suddenly ALL tables have 6 random character prefix automatically added to entire DB tables!

So now instead of having one table.. wp_usermeta
I now have.. aojsfj_wp_usermeta

Now, opening for example aojsfj_wp_usermeta is not a list of users, it’s just ONE user’s meta. So now the DB has created all separate tables per the few (7) test user accounts, prefixing them with 6 random characters.

Can someone enlighten me on why / how this has happened? So far everything still seems to be working, but the DB + all these new tables can’t be good!