I am not completely sure, but I think it is the "General Import" Translator.
You can try Merging the IFC file. In that case, you can select the Translator to use, Select the General Import Translator and see if it gives the same result as the drag-and-drop. If it does then it is most probably the "General Import" Translator.
Or change some setting in the "General Import" Translator before doing that drag-and-drop so you can absolutely positively tell whether that was used by the drag-and-drop or not.
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