Theophylact of Ohrid

Some of them that stood there, when they heard that, said, This man calleth for Elijah. The multitude did not understand His cry, being uncouth and ignorant of the prophets, and thought that He was calling upon Elijah. For not all the Jews knew the prophets, just as now not all Christians, perhaps, know the Gospel.

Commentary on Matthew ↗

Jerome

But some of those standing there, when they heard it, said: This man is calling Elijah. Not all, but some whom I believe were Roman soldiers, not understanding the nature of the Hebrew language, but from what he said: Eli, Eli, thinking that he was calling Elijah. But if we want to understand the Jews who said this, they do this in their usual way, to dishonor the Lord of weakness, who invokes the aid of Elijah.

Commentary on Matthew ↗

Thomas Aquinas

Then the effect follows: "and some that stood there etc." And first, the common effect in all is set forth; second, in one of them, at "and immediately one of them running etc." He says therefore "and some of them that stood there and heard, said: this man calleth Elias." Who were these? Jerome believes that they were soldiers who did not know the Hebrew tongue, and because of this they believed that he was calling Elias, because Elias was very famous, since he had been taken up into heaven, as is found in 4 Kings 2:11. …

Commentary on Matthew ↗

Rabanus Maurus

The soldiers misunderstanding the sound of the Lord's words, foolishly looked for the coming of Elias. But God, whom the Saviour thus invoked in the Hebrew tongue, He had ever inseparably with Him.

Catena Aurea by Aquinas ↗