The burnt/scorched looking leaves could mean a lot of things. My first guess would be over fertilization either at the nursery or by you. Blueberries need acidic soil at a pH level of about 4.5-5. If you used a regular high nitrogen fertilizer, it would be terrible for the plant and the leaves can get "burnt" from the fertilizer.
Secondly, blueberries like well drained soils. They have very shallow root systems and stagnant water can also lead to discoloration of the leaves, although this is usually deep reddish-brown (like fall colors), and seldom have a burnt appearance. However, I won't rule this out. Since you said that it was heavily rootbound, it is very likely that the water wasn't draining away fully. I explain a bit more about this and how to increase soil pH for blueberries in this answer
Unfortunately, reddish leaves are also a symptom for underwatering! From Mike Perry's answer to my question on boysenberries
Below quote comes from Growing Small Fruits for the Home Garden:
Lack of supplemental watering from June to August severely limits successful production of blueberries in the Pacific Northwest. Shallow-rooted plants require close attention to maintain a uniformly moist environment around their base. They require 1, or possibly 2 inches of water each week, in the absence of any rainfall. Be sure the entire root zone is wet after an irrigation. Drought symptoms include reddened foliage, weak, thin shoots, and reduced fruit set. Maintain a 2-inch mulch layer to preserve soil moisture.
Also see the scientific reason in Mike's answer, although I'm not sure if that applies to blueberries too.
Lastly, it could be something as simple as sun scorching. If the nursery was in a place that had long periods of direct, intense sunlight every day, it could have scorched the leaves. This happened to my raspberries and the advice there was to use a sun shading fabric.
In any case, from your description, the plant seems to be doing well in your garden, so you probably are doing things right. :)