Yeah, I don't think it necessarily implies they used them before but there's nothing that directly contradicts it either. Certainly open to interpretation.
On a tangent but since we know space fighters such as X-wings can fly quite capably in an atmosphere (TFA certainly emphasizes this) I do wonder what purpose combat airspeeders really serve. Of course the real answer is obviously "it's just a movie", but my head-canon had always assumed there was some technical reason (greatly reduced atmospheric performance, etc) they didn't use X-wings (or any Y-wings present but not seen) against the AT-ATs on Hoth but TFA kinda dispels that notion.
I think the only reason they didn't use them is because they were using them to protect the transports. The goal of the speeders was just to slow them down as much as possible while everyone else bugged out, plus the speeders were probably a lot more maneuverable in close quarters. Why throw those precious x-wings and y-wings at them when they are really needed to be keeping ties etc off the transports