Did not God directly, but God via an angel talk to Moses on the mount Sinai? Is there anyone other than Paul explaining this was communication from God through angels?
Calvin has this to say about Galatians 3:19 :
Ordained by angels. The circumstance, that it was delivered through angels, tends to the commendation of the law. This is declared by Stephen (Acts 7:53) also, who says, that they had "received the law, (eis diatagas angelon,) into the dispositions of angels."
. . . in which Calvin quotes Stephen saying (in full) :
Which of the prophets have not your fathers persecuted? and they have slain them which shewed before of the coming of the Just One; of whom ye have been now the betrayers and murderers: Who have received the law by the disposition of angels, and have not kept it.
[Acts 7:52,53 KJV]
Of Acts 7:53, Ellicott has this to remark :
By the disposition of angels.—Better, as ordained of angels; or, more literally, as ordinances of angels. The Greek preposition cannot possibly have the meaning of “by.” The phrase expressed the current Jewish belief that angels were the intermediate agents through whom Israel received the Law; that it was their voice that was heard on Sinai. Here also St.
Paul, in speaking of the Law as “ordained by angels” (Galatians 3:19), reproduced St. Stephen. Comp. also Hebrews 2:2 and Jos. Ant. xv. 4, § 3, for like statements. The idea rested mainly on the LXX. version of Deuteronomy 33:2, “on His right hand were angels with Him” and “the thousands of angels” as connected with Sinai in Psalm 68:17.
The writer to the Hebrews also expresses the same :
For if the word spoken by angels was stedfast, and every transgression and disobedience received a just recompence of reward . . . etc.
[Hebrews 2:2 KJV.]