Yeah, that's one of a few reasonable explanations if these news are true. If all the factories are already full, then it makes sense to just buy the excess demand from other countries, especially considering that those are pretty simple drones that probably don't need extensive integration or state-of-the-art specs.
Another possible explanation is that Russia is buying those drones through Chinese shell companies but in that case why would Iranian government publicize such a thing when their modus operandi so far has been officially denying that they sell the drones to Russia?