“They said to one another.
‘Is it because
We brought no bread?’”
οἱ δὲ διελογίζοντο ἐν ἑαυτοῖς λέγοντες ὅτι Ἄρτους οὐκ ἐλάβομεν.
This is exactly the same, word for word, as Mark, chapter 8:16. The disciples were still worried that they had forgotten to bring any bread. They did not understand the warning from Jesus. They said to one another or reasoned (οἱ δὲ διελογίζοντο ἐν ἑαυτοῖς λέγοντες) that Jesus must be talking about their failure to bring the bread (ὅτι Ἄρτους οὐκ ἐλάβομεν).