Why should Peter have stopped quoting Joel at Acts 2:18?

Les teaches that Peter had already said this was what Joel spoke, and it was happening on the Day of Pentecost. But after verse 18 Peter should have stopped, had he known Israel was going into dispersion and God was going to turn to John. He did not stop. He was still hanging tooth and nail on the Old Testament program, believing Israel had to come to a knowledge of their Messiah, then the tribulation could unroll, and then they would have the King and Kingdom. So he continued into verse 19, quoting Joel about wonders in heaven, signs in the earth, blood, fire, vapor of smoke, the sun darkened, and the moon turned to blood before the great and notable day of the Lord. Les identifies that as the tribulation. Peter knew it had to come, but he kept quoting, and the passage ends with whoever calls on the name of the Lord shall be saved; Les notes that this is Peter, not Paul.