It could be - their acidity could be causing the spilliness, and their fibrous texture could be causing the runny poo's ... I'm no expert, but if the symptoms hadn't been happening before the feijoas, it sounds highly likely.
Everything in moderation!
I

feijoas too - what stops me from eating them by the truckload is that they're $10 a kilo down here

(last year, when pregnant, I was living in Hawkes Bay and I almost lived on them!)