Even if the OP was "only" a distance runner in his past athletic experience, and has "only" been running 5 mpw (which says little about being ready to run fast, certainly, but still means you are more active than at least 2/3 of the population), that's going to suggest more potential for running fast than your average Joe who may or may not have gotten off the couch more than 2-3 times a week in the last decade.
I'd assume that the average 100m time for the average adult in the US after a year of pretty decent training would probably be closer to 15 seconds. For only "casual" training (which I would consider to be 2-3 times a week without much structure or plan), probably more like 16-18 seconds, and even that is probably optimistic (such as, either discounting the very obese or those that couldn't train without getting injured within the first couple months and calling it quits).
Being sedentary is better for your 100 time than being a hobby jogger or a serious distance runner. This isn't a 400; you need speed and explosiveness that's hindered by low mileage jogging or high mileage running.
The standing vertical jump of elite marathoners is something like 12"-13". The corresponding figure for sedentary folks is more like 18"-19". Anecdotally, I know some distance guys who set PRs in the 200 after having to take an extended time off due to injury, burnout, or work demands.
Even if you assume that jogging 5 MPW helped the OP improve his time, there's no way it helped him get from a 15-16 second 100 (your guess for an average adult's capability) to a 12.38 FAT. That's a lot of difference.