I'd vote "happy coincidence" with a measure of "isn't physiology funny?" Pretty common to have this kind of thing happen... Kids' bellies relax in the tub with all that warm water, the toots start, and we all know what is likely to come next! However, that doesn't mean you can't use this to your advantage as long as she is happy and excited to sit up there!
--Mimi
Mom to Lala (2004), Bonus Mom to Big Sis 1 (1991) and Big Sis 2 (1992)
Grammy to Big Kindy Kid (2011), Big Pre-K Kid (2012),
Grandbaby Appendage (2014), and New Baby Grandboy (summer 2017)