You obviously don't know much about being a Christian. Just because I am a Christian does not mean I am to sit down and shut up. I am allowed to speak of my God. I did not boast of knowledge, or worldly actions, I did not try to call anyone out and claim they were boasting or needed scripture discernment..
As for your quote from 1 Corinthians 3: 21 
boast in men. Cf. v. 4; 1: 12. Paul, Apollos, and all others receive no credit for the building of the church. all things are yours. All believers share equally in God’s most important and valuable provisions and glories; human boasting, therefore, is ludicrous as well as sinful." 
You see, I did not boast, I did not claim I did anything or changed the election by my power, that my friend would be stupid and boastful. I simply stated that we Christians prayed, that our God has the power to fulfill His will. 
 
I am allowed to claim my God hears and answers prayers, because my God has said it is so.