[bicycletricycle]

The wheel bearings and freehub both bound up?

And with a simple loosening of the wheel bearing non drive side cone both freed up?

Hmmm, the easiest explanation is that one of the wheel bearing cones unlocked from its locknut and crept inwards preloading the bearings till they where seized.

However

I don't think that this would seize the freehub as well

the free hub bearings are not adjustable and shouldn't be effected by the preload of the wheel bearings.

The freehub has a washer between it and the hub shell, if it is missing than normally the freehub just seizes up as soon as you tighten up the huge hollow Allen bolt that holds it onto the hub shell.

If for some reason the large hollow bolt that attaches the freehub to the hub shell came loose it might cause the problem you are having.

If someone forgot the washer or used the wrong one than perhaps they didn't torque the freehub down properly to keep it from seizing.

So, either the freehub came loose or the cup and cones tightened up.

I'm betting the freehub came loose, it explains the bearing and freehub seizing more easily than just the hub bearings.

Get the huge Allen wrench and do it yourself this time.

IMHO