I generally dont accept drinks from guys even when my guy is at home. One reason is that guys will generally make outbursts like that even if you stay and chat with them because they've had a few drinks already (which has happened quite a bit to me even though I'm polite, state that I have a fiance beforehand ...even though I dont... and even show them my gorgeous "engagement" ring... and also accepted drinks because I'm usually pressured from my gf so she can chat with the guys friend etc) or want to still get at you like one of my ex guy friends. He purposely tries to get the girl thats taken already... he said its funner that way... suffice to say thats why we dont hang out anymore... he'll hit on me only when I'm have a bf... so no talky at all anymore.

A few of my gfs do that all the time though, and I feel really bad for the guys... really uses them and we take off... and thankfully they usually drive when we go out cause I did get drugged once because one accepted drinks from this guy for the whole group. So no more drinks from strangers for me.

So maybe that guy did just want to chat, or maybe he was seeing if you'd have a fling before the big day. Who really knows? Human beings can be pretty heinous. The only way to prevent anything like that is just politely refuse because you never know, they can be the most polite and sweetest guy and just not give any hints of anything til you get the drink and dash cause they wanted something but you didnt save for the drink.