I tend to agree with John F. Likely some friends maybe did you a favor and stocked one or a few LMB for your new pond. However - some of the fastest growing LMB from your fingerlings stocked in LA with abundant forage could feasibly get to nice size in one year.
Dr Willis noted that
average growth of southern bass at one year old was 6.5" and at two years old is 10.0". Note these are average lengths for southern bass; not the fastest growth. Using the same reference (Carlander) as that used by Dr.Willis, the largest one year old LM bass from various studies in southern states ranged from 11.8" to 14.9". We should assume that the fingerlings that were stocked in were hatched in spring 2014 and growth that you are reporting is for individuals that are 20 months old; May-Dec2014 8 months and Jan-Dec 2015 12 months = 20 months. Actually 3"-4" LMB procured in December are IMO somewhat slow growing and could have easily been by December2014 6"-8" long if not crowded and provided excess food all summer-fall.
Greg Grimes posted this for some good growth of LMB in SE US.
"To let you know for our clients (in the SE, lower altitude)wanting "good" bass fishing I expect:
1 yr- 11 inches
2 yr- 15 inches
3 yr- 18 inches
4 yr- 20 inches
5 yr- 22 inches
>6 yr ?-
we get growth rates much better than this routinely."
In optimum forage and habitat conditions Greg has measured the following of growth for maximum growth rate of the fastest growing LMB: in one year (12 months) fingerlings in the south could grow to 2.48 lbs (15.6") and in 17-18 months 4.8 lbs. Note not all the bass from the initial stocking were this large just a few of the ones that grew the fastest - sometimes called 'shooters'.
http://lakework.com/wp-content/uploads/2013/01/sdafs-trophy-lmb.pdf 
