Paul is opposed to boasting and under normal circumstances he would never do it. This the same Paul who wrote, ‘Let nothing be done through strife or vainglory; but in lowliness of mind let each esteem other better than themselves (Philippians 2:3).
Don’t be surprised if error comes from those with much orthodoxy. False Christians are often wicked people. Maybe they want a following, but they often deceive many true believers. It is even more dangerous if you know and trust them.