That passage says--the inhabitants of the earth are burned, and few men left. If taking this part--the inhabitants of the earth are burned, to be meaning the entire planet is literally engulfed in flames, as in every square inch of it, that verse would not then be saying, and few men left. It would be saying no men left, as in zero, since no mortal could survive if every square inch of the planet is literally engulfed in flames the same way every square inch of the planet was engulfed in water during Noah's flood.
Well it does not specify if every square inch is burned, but it does specify that a few men shall be left. We also see below that some of the people of the nations remain during the millennial reign of Christ on earth.
Zechariah 14:12-21
King James Version
12 And this shall be
the plague wherewith the Lord will smite all the people that have fought against Jerusalem;
Their flesh shall consume away while they stand upon their feet, and their eyes shall consume away in their holes, and their tongue shall consume away in their mouth.
13 And it shall come to pass in that day, that a great tumult from the Lord shall be among them; and they shall lay hold every one on the hand of his neighbour, and his hand shall rise up against the hand of his neighbour.
14 And Judah also shall fight at Jerusalem; and the wealth of all the heathen round about shall be gathered together, gold, and silver, and apparel, in great abundance.
15 And so shall be
the plague of the horse, of the mule, of the camel, and of the ass, and of all the beasts that shall be in these tents, as
this plague.
16 And it shall come to pass,
that every one that is left of all the nations which came against Jerusalem shall even go up from year to year to worship the King, the Lord of hosts, and to keep the feast of tabernacles.
17 And it shall be, that whoso will not come up of all
the families of the earth unto Jerusalem to worship the King, the Lord of hosts, even upon them shall be no rain.
18 And if the family of Egypt go not up, and come not, that have no rain; there shall be
the plague, wherewith the Lord will smite the heathen that come not up to keep the feast of tabernacles.
19 This shall be the punishment of Egypt, and the punishment
of all nations that come not up to keep the feast of tabernacles.
20 In that day shall there be upon the bells of the horses, Holiness Unto The Lord; and the pots in the Lord's house shall be like the bowls before the altar.
21 Yea, every pot in Jerusalem and in Judah shall be holiness unto the Lord of hosts: and all they that sacrifice shall come and take of them, and seethe therein: and in that day there shall be no more the Canaanite in the house of the Lord of hosts.”