Since you have been born you had to be born on some day, the probability that you were bone on your birthday is 1 (effectively by definition).

Here the 18th of December is selected as of interest precisely because it is your birthday, so it is not surprising that you were born then.

(the 1 in 365 is the probability not the odds. Odds (at least mathematically and at my local bookies) are defined as the ratio of winning chance to losing chance, so in this case would be 1 in 364 ignoring leap days)

CB