Interviewer called my previous employer. Is this a good or bad sign ?

Okay so I can't even count how many jobs I've applied to. Maybe over 300. Almost 95% of them ended up being rejected. However, two days ago, a company I had interviewed for, first over the phone and then in-person emailed me asking me the phone number for my previous employer. I gave them the details, and the next day I emailed my previous employer to expect maybe a call. To this they said that someone did call asking about me.

Till now, I have not reached this point in any interviews were they call my previous employer. I don't know what to expect next. I had a really good relationship at my last job. And I know for a fact they said pretty good things about me. So I'm wondering what can go wrong at this point ?

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