Getting bigger and getting stronger may seem like they are the same thing, and in many ways they are very much complementary to each other, but manipulating certain training parameters can yield different results depending on your training goals.
Simply put, maximizing muscle size requires a range of rep between 8-12 per set, and usually requires a relatively large number of sets (volume) compared to that of strength training. On the other hand, maximizing strength, which will still yield size gains requires between 3-6 reps per set, and usually does not require many sets (volume).
Now, if you train to maximize size, you will no doubt get stronger, but you are working more on strengthening your muscular system rather than the nervous system, which is heavily taxed in strength training. If you train for sterngth, you will no doubt get bigger muscles, but those muscles will not likley reach their maximum size. Instead, your nervous system does quite a bit of lifting to support your muscles in lifting heavier loads in the range of 3-6 reps.
Know yourself, know your goals, and train accordingly.