Current tabs removed, and old tabs reappeared in Safari

So today my Safari just randomly removed all of my current tabs (about 30 of them) and replaced them by the tabs that ive had abiut a year ago. I would imagine that all of the tabs that i had are now gone, but why did that happen?

Also a very interesting thing i have noticed. I always use private mode in Safari. So considering that all of the tabs from a year ago just reappeared, does that mean that you guys collect and keep all of the search information from our private search for years? Otherwise how can you explain that?