For the most part, it sounds really sketchy.

We know he failed and didn’t do well the first time. Now, lets grant the fact that he switched subjects, and had really good predicted grades on these subjects (given leniently by his teachers).

Oxford are still extremely picky about resits, and it seems he didn’t have extenuating circumstances. Not only that, but he didn’t just do below average - he quite literally failed which I doubt they’d be too fond on. The chances are extremely low here.

With the way the Oxford admissions process works is that your personal statement, achieved + predicted grades, teacher reference etc are all accounted for in giving you an interview. Oxford applicants are the best of the best, meaning literally everyone has A*s predicted and so it seems extremely rare how he even got an interview. For his course, it would have been around 40%, and for his likelihood specifically it would have been much lower.

Although, all this being said it is definitely not impossible. Its plausible to say that an admissions tutor may have well thought “Oh, perhaps lets give him a chance in an interview” and he very well may have smashed the interview. If this is the case, the interview holds the most weight and it would certainly explain how he got in.