Bounding box is stroked
My system: iPad Pro model MLMY2LL/A running iOS 14.1; illustrator for iPad version 1.0.0 (just updated today but version number has not changed).
In the attached file I made a figure, duplicated it, and changed the fill to null and the stroke to black. This operation resulted in the selection bounding boxes being stroked as well.
How I made the original figure: created a text word, converted to path, combine all to connect overlaps. Duplicated the figure, flipped the dupe vertically, moved into position and grouped with original figure. Selected all, chose Radial Repeat and fiddled with options to get the final figure. Object...Expand to get the final version of the figure (grouped).