Would this be possible on the BKK-SIN-BKK flights?

I flew BKK-SIN two weekends ago in J (paid) and will fly next week back to BKK in J (again, paid, and on the same PNR). On the outbound, the entire F cabin was empty - this surprised me because I had bought the ticket at the TG Suvarnabhumi reservations office due to missing an SQ flight to SIN, and I had asked if paid F was available (it wasn't).

Would they have been allowed to assign seats in the front F cabin? I was given 11K when I asked for the 'most front, to the right' of the aircraft... or is it more likely that the J check-in agent only start checking from Row 11?

I did not OLCI, as I felt no need to seeing as I'd gotten what I thought was the 'most front, to the right' seat available.

If they are allowed to do so, I'll surely ask for Row 1 next Friday back to BKK.

(Oh, if it is relevant, I'm *G with BD)