Spiking Drinks?

Sup peoples. I have a question for youse.

I'm a dude, and was in a nightclub last night (which was pretty dead to be honest), and was sitting on a couch waiting for my mates to get back from the bathroom.
There was another dude sitting on the couch with a glass full to the brim of some sort of beer on the table, who was alone waiting for his mates. Suddenly, he turned to me and said that I can have his drink cause he doesn't like beer.
I thought it was fairly odd that he would have ordered the pint in the first place? Anyway his mates came over a few seconds later and went off to dance, leaving the untouched beer on the table.

Now, if I was a girl, then I probably would have jumped to the assumption that it was spiked, but I'm not, so...?
My mates advised me not to touch it (and I didn't) but what do you honestly think that guy was trying to do?

It's that lingering paranoia in the back of our minds that makes it hard to trust people...