What will have happened is this:
The beer can when placed on the table will create a seal of air in the concave indentation at the bottom of the can. Presumably there is a seal of moisture around the base, either spilt beer/condensation/slavers/drool.
The air pocket will heat up and expand (as most things do when heated), thus forcing the can off the table - but wait! the seal of moisture traps the air in for slightly longer and lifts the can, also the mositure provides a slicker surface for the can to mvoe more freely, as the air escapes/cools, the can then comes back down to rest a few inches away. The desk is most probabbly slightly slanted as well.
this is the same trick with a 5p and a becks bottle. 1. Drink beer. 2. get 5p and slaver/drool all over it. 3 place slaiva soaked 5p on top of bottle. It should fit snugly, sealed ith the spit. 4. Hold hands on bottle. 5. in about 10-20 secs, the 5p will jump and lift and wriggle about, as the warmer air in side expands and escapes.. <and breathe>