If you punt often enough it's likely to happen.
Majority of WGs will not initiate contact or indicate they know you unless you make the first move. And some will simply not remember you given the volume of clients.
If you're by yourself, it's no big deal. I met a WG I'd seen in the supermarket but she didn't recognize me and I didn't say anything. It wouldn't have bothered me if she had though.
If you meet a WG in public while you're in company, that's a more risky situation. But again the WG will seldom acknowledge you unless you make the first move. If you need to introduce them to your partner, just say they're 'X from work'. If you're with work colleagues, just say they're 'X, a friend'. Nobody knows what they do or your relationship with them unless you act guilty.