Yep, relapse...and as was so kindly pionted out, it's the actions and behaviors prior to picking up aka; relapse mode.
Had your friend actually found the real thing that would have been active using.
I am always confused by people who say they relapse after being clean for a week or two, because I can't phathom what changes actually occured in such a brief period of time. Our attitudes and behaviors which took years to instill cannot be changed overnight. It takes time and effort to become a "different" person. The way we act and react to all the situations life presents. Relapse is a returning to old behaviors, a slip is picking up after a sober spell.
That's my take on the whole thing.
Hope your day is a pleasant one
Larry