did they say photoperiod or autoflower?
"fast" can indicated that it was bred with ruderalis in hopes it made it flower faster, but still be a photoperiod. this is a false hope. Autoflowers are not actually faster to flower. People just erroneously don't start counting days until 1-2 weeks after it has alreaday entered flower, because they are relying on what they see.
7-9 weeks is normal. Most will be 8-9 weeks whether labeled as "fast" or not. some can take longer, too, but not relevant here. You don't need to infuse weak ass ruderalis genes to get a 7-week flower period. you simply need to put in the effort to select for that trait and make it consistent in the offspring.
faster flower correlates to lower yield too, fyi. Same variance in yield output due to genetics as always... some "fast" plants will still yield very well.