Some strains have hollow stems, so that shouldn't be an issue. I've seen that type of damage from higher humidity and foliar feeding, where the water gets trapped between two leaves and the damage appears at the main points of contact (on top of the leaf ridges). No chance of spider mites, right? They can cause damage somewhat similar to this, but there are usually tiny red dots on some of the larger fan leaves in addition to the rusting. The damage probably happened at least a week or 10 days ago... it can take that long to appear. Deficiencies can cause some issues as well, but this doesn't look like a deficiency or an overdose, at least to me. What medium are you using? It's kind of hard to tell from a single photo of a leaf, but it is probably OK. I'm not one for pouring stuff on a plant to try to counteract something else that was put on the plant previously, but maybe a dose of foliar applied
cal-mag might help. The leaf looks non-specific to me, so I'd just let it grow and see what happens rather than trying to figure out what, if anything, that you did to it.