Hi welcome!
Well that's what rehab is for. A couple of short rehab starts should reveal his progress. We really need him as a starter and more importantly a workhorse to get the rotation going deep in ball games again or our BP is going to be dead by August.
I don't think they could have predicted his K rate would be cut in half and there's no way they expected this type of return but perhaps they saw potential for Smoak to be a poor man's Chris Davis with a full time gig. We often forget that $4MM/yr isn't a very big contract in the overall picture and the possibility of losing EE/Bautista was sort of a big deal back then.