Yeah there would be a mini cycle but he isn't going to set up the new tank, move over the filters and let it sit for a week with everything in the old tank and no filter. If it were me, I'd move everything over (except the sand) and then just carefully watch the parameters so if they get anything too bad do a PWC
. Honestly though, the vast majority of the beneficial bacteria is on the filter media (yes there is some on the glass and sand) so I think everything will go smoothly.
Oh, do you have live rock as well? That would further minimize any mini cycles.