Yeah, they didn’t describe the calls in that article, but I their spectrograms are in the original paper. It seems that they tested two different foreign calls from the same species. They compared these two calls to local alert calls and a couple non-alert call controls. These two foreign calls were actually a bit different, one increased in pitch as you predicted. But surprisingly, the other one started fairly high and decreased in pitch(although this one did seem to have a bit more power). Neither of these 2 were nearly as high pitched as the local alert calls, but both were quite a bit higher than the controls.

Edit: I tried to put the spectrograms here, but I think it’s not working. They are in the paper though.