Prophecy has its own language of symbolic meanings. Thousand is not the number it seems to be. The Greek word chiliads or thousand can also be used as a tribal or people group designation in the Septuagint or LXX. The Hebrew ‘elef can mean both thousand or clan/tribe.

These were the ones chosen from the congregation, the leaders of their ancestral tribes, the heads of the clans (‘elef) of Israel. Num. 1:16

The Greek LXX follows the Hebrew

Moreover choose able men from all the people, such as fear God, men who are trustworthy and who hate a bribe; and place such men over the people as rulers of thousands, (chiliarchos) of hundreds, of fifties, and of tens. Ex. 18:21

35  And whenever the ark set out, Moses said, “Arise, O LORD, and let thy enemies be scattered; and let them that hate thee flee before thee.” 36 And when it rested, he said, “Return, O LORD, to the ten thousand (revavah) thousands (chilias) of Israel.” Num. 10:35-36

FYI: The Hebrew ravavah means myriad, multitude, or ten thousand.

I will take away its blood from its mouth, and its abominations from between its teeth; it too shall be a remnant for our God; it shall be like a clan (chiliarchos) in Judah, and Ekron shall be like the Jebusites. Zech. 9:7

The same use of the word appears in the New Testament in the Bethlehem prophecy.

But you, O Bethlehem Ephrathah, who are little to be among the clans (chilias) of Judah, from you shall come forth for me one who is to be ruler in Israel, whose origin is from of old, from ancient days. Mic. 5:2 

‘And you, O Bethlehem, in the land of Judah, are by no means least among the rulers of Judah; for from you shall come a ruler who will govern my people Israel.’” Matt. 2:6 

A Large Number

When it is doubled it means innumerable.

Then I looked, and I heard around the throne and the living creatures and the elders the voice of many angels, numbering myriads of myriads and thousands of thousands, (chilias, chilias)) Rev. 5:11