I have a tabasco that was severely stunted. the person who gave me the seedling had it in a half inch of soil for over a month. when I got it, it only had 2 leaves on it. I repotted it into a bigger pot, but the stunting was severe. it's 8 months old now, and only about 8" tall. it's bushy as hell, but short. I've gotten over 100 pods off it, but the pods are all undersized too. it's like a pepper bonsai. I like it, it's kinda cool. there are many factors that determine how long after transplant it takes to recover, but it may always be a small plant. in the grand scheme of things though, it's not that big of a deal for it to be small. you'll still get peppers. well, if you have enough time before frost, that is.

peppers are pretty good at bouncing back from tough growing circumstances. I had some that I had uppotted into some pretty bad soil.. stopped growing for months, lost color, and lost a few.. but once i repotted in good soil, they turned green in ~2 weeks, and kept growing from where they'd left off.

You said a few weeks? The leaves in the pic are still somewhat little discolored. have you fed it since you planted it?

When I repot / transplant root bound plants, I try to loosen some of the roots and even maybe CUT some of them to give the plant a jolt.
This way, IMO, the plant will realize a change and will try to adapt to the new environment. If you do not disturb the root system, it will not affect the plant for a long time.