If you said it was marginal winds, with an efficient foilkite and faster wing, yes, it can definitely happen that you can not go upwind when on the mere verge of "just" being possible to foil, especially if not a big wing.
As others have said - you will shift the wind window a lot with speed, and with good gear and technique you MIGHT just be able to foil, but without going upwind.
Have tried this myself, and seen race mates too, in this very situation.
But as you said you felt powered, above is hardly the case, but more likely one of, or both of, two things:
1. Strong current, that goes without saying, but I assume you dont have current since you dont mention this yourself as by far the most evident ?
2. Microbubbles in the wind - so there is less pull and no efficiency, even though you feel powered.