I call BS. Why would they hire you at an agreed to price, go through the cost & effort and then try and "get you"? Your old neighbour was either in bed with his hiring clients or not very good at his job.
I know of many people who were fired the day their guarantee elapsed- I can’t think of a single person on a guarantee who was fired before then. To put this into context, we had a guy on a guarantee on our prop desk who came in for one week after he joined, put on a (massively winning) trade that got him enough to get his guarantee and then literally didn’t set foot in the office for the rest of the year[1] until the day he came in to collect his bonus and resign/be fired.
[1] And it’s not like he was working from home because people in trading were (for compliance reasons) not allowed to work from home unless there was an emergency like a terrorist incident where the trading floor was closed.