Given no other information I don't knows if there's much more you can say about it. You can look at this selection rules table on Wikipedia and see which types of excitation can drive this transition. As you point out parity is conserved so that rules out odd multipole electric transitions and even multipole magnetic transitions.
This leaves for example magnetic dipole, electric quadrapole, magnetic octopole, etc.
The other piece of information you have given is that $\Delta m_J = -1$. This basically doesn't rule out anything. If instead it had been $\Delta m_j = \pm 2$ then that would have ruled out magnetic dipole transitions.
However, it is of course worth pointing out that which transition you are driving depends on the multipolar decomposition of the electric/magnetic field you are driving with. For example, if the field is uniform across the entire atom (which is of size ~$a_0$) then the field can basically be expressed entirely as a dipole field. This means the excitation photons have the mode function of a dipole field. In this case ONLY dipole transitions are driven. If the field has some gradient across the atoms then it now includes quadrapole components which drive quadrapole transitions.
Once you determine whether the field configuration includes dipole and quadrapole elements you must now calculate the transition matrix elements for the different types of transitions you are considering. This is basically to say how well does my ground state, when I act the dipole, or quadrapole operators on it, overlap with the excited state. It is a geometric statement about the ground and excited states. It turns out (perhaps I can give a more thorough explanation why at a different time) that these matrix elements are increasingly suppressed by certain large factors as you move to higher multipole orders.
So to answer your question, it is most likely that you are driving a magnetic dipole transition here. This is because
1) It is allowed by the selection rules (and electric dipole isn't allowed)
2) It is the lower order multipole excitation which is allowed which means it has the largest matrix element of all multipole transitions
3) You are most likely driving the transition with a field which is predominantly dipolar from the perspective of the atom. I don't know how you would get an RF field which varies dramatically over a length scale of $a_0$.
However, if you were a bit crazy, you could try to build some RF emitter which could realize a significant field gradient and try to drive this transition by, for example, an electric quadrapole transition. Perhaps you could do it with some small atom chip with tiny wires layered on it. I think if you got the polarization and frequency right you could try to drive purely $m_F = \pm2$ transitions which could be evidence that you are excited it via an electric quadrapole transition and not the easy magnetic dipole transition.