How could Dev have possibly recognized the Sanyasi as Sai Baba? The man appeared before the meal to collect funds for cow protection, so why would Dev assume this fundraiser was the saint he invited?

Dev's failure to recognize Baba was a result of a 'state of delusion' as described in Chapter 40. The sequence of events was indeed confusing. The Sanyasi first appeared to collect funds before the meal, which led Dev to fix in his mind that he was just a guest seeking money or a meal. Dev himself later lamented this, noting that since the first visit was for fundraising before the Udyapan invitation was even sent to Sai, the delusion occurred. Baba explained to Jog that this first visit was to remove Dev's fear of being asked for money, while the second visit with two others was the fulfillment of his promise to attend the meal.