You should have noticed that 'first accusers' was in quote marks. This should give you pause.
Socrates' first accusers, he says, are the people of Athens in general and not Meletus. See §18a. These accusers include Aristophanes who ridiculed Socrates in his comedy The Clouds.
His response is to remind the jury, who are the people of Athens themselves, that they have grown up hearing things about "a ponderer over the things in the air and one who has investigated the things beneath the earth and who makes the weaker argument the stronger” and to remind them that rumours are not always the truth.
The lesson here is: