Giovanni Visconti — according to Lorenzo Cardella nephew of Pope Gregory X. He was ostensibly created cardinal-bishop of Sabina by his uncle in 1275 and in 1276 was named judge in the case concerning the translation of bishop Giovanni of Potenza to the archbishopric of Monreale, postulated by the cathedral chapter of Monreale. He died in 1277 or 1278.
Lorenzo Cardella is not the nephew of Pope Gregory X.
Giovanni Visconti is the nephew of Pope Gregory X, and the context is relating the history according to Lorenzo Cardella.  So, this statement is true. The context is oddly worded, and confusing, so, it was likely that which tripped up the system.