It's generally bad practice to reward fate points for rolling well. It would probably be better to give them a fate point for having a great plan and then seeing it fail horribly by bad luck.
I didn't really ask your opinion on whether it was a good idea to do it, but they didn't have a good plan either. Bad luck happens that's why I don't like Fate in general, especially when players use a fate point and then proceed to fail again.
Ooh, someone's saucy. Just offering some advice. Rolling really well is reward enough. Having terrible luck but then getting a temporary fate point afterward (I should clarify that the fate point would not be usable on the failed roll) is a way of rewarding players for bad that actually encourages them to take risky plans and so on mechanically.