It weakens the bond of THC at the receptor sites on the CD1 and CD2 receptors. I think all chemistry is physics really. Whether the bond is chemical or mechanical it is safe to say CBD ‘knocks THC off’ the receptors.
And yes, CBD cigarettes (cannagarettes? Anybody?) are smoked as first aid for overdoing it with the THC. It helps @Sugarleaf immensely. Also good first aid for this is massive (10-15000mg) doses of a good vitamin C. This helps your liver to metabolise the THC and get some clearance going on your blood stream.
Interestingly, CBD knocking THC off of the CD1and2 receptors isn’t where the story ends for the THC. CBD also inhibits the liver enzyme that breaks THC down. This means that while THC may have a weaker bond with these receptors (which are all over the body by the way, in every organ) it stays in circulation in the body for longer, allowing it to do more, theoretically, than it might have.