Your buddy is totally right. We always force carbonate, so we blast it with CO2 anyway. But many times, you'll catch a leak that way. And we have some kegs that won't seal unless you pull up on the lid while blasting in CO2. That seats the seal, as your buddy describes, and they hold fine after that.
Oh don't give me none more of that Old Janx Spirit
No, don't you give me none more of that Old Janx Spirit
For my head will fly, my tongue will lie, my eyes will fry and I may die
Won't you pour me one more of that sinful Old Janx Spirit