Ovulation is a very tricky thing. Like Annie said there's vast differences between all women.
Women actually will ovulate roughly 10-14 days BEFORE their cycle is due to come on. For example, a female with a 34 day cycle would generally expect to ovulate on or around CD 18-24. Using 10-14 days after their cycle would place it as CD 10-14. (This is also why many women have difficulty getting pregnant - they assume the wrong dates) There is a lot that needs to be looked for when guessing, so it is actually very possible she could have gotten pregnant like described.
Annie brooke said it all.... its very likely hes the dada..
It is possible to learn that you are pregnant two weeks after sleeping with someone. (It's even possible to learn it less than two weeks after sleeping with a sensitive pregnancy test or get a blood hCG test.) You are confused because you are saying ovulation is 12 to 14 days after the first day of the last period? That is true but only on average. Individual women swing widely around the average, and can ovulate early or late. (My little sister for example always ovulates on day 8 of her cycle [i.e., 8 days after the first day of bleeding].) You said the person met the guy on the 13th of March, and was "coming off" (I assume that means her period was ending) at that time. Then slept with the guy on the 14th of March, and you are thinking this was too early for ovulation? Let's say she was on day 6 of her cycle on the 14th. She could have ovulated any time between then and day 11 (which is not unusually early) and gotten pregnant by the guy from the event on the 14th of March, since sperm can live up to 5 days at least, in a woman's system. And with a blood test or an early-results test, the pregnancy could be detected on the 28th.
If you really have an oar in the water here (i.e., this is your brother's child or your husband is being told by someone that he impregnated her), you can suggest to the guy that he has the right to request a DNA test before automatically assuming the baby is his. But if you don't, then in your shoes I would not stir the pot. It's possible, not guaranteed but possible, for what the person says to be true.
that confued me to im not really sure