If you distribute a program based on GPL sources you have modified, you have to also distribute that source code. That is, unless the original authors gave you the sources under a different license.

He is right. If you modify and distribute GPL code, whatever changes you made have to be distributed with it in source code form. The BSD licensed code doesn't have this restriction, which is why it's used in place of GPL for those not wanting to redistribute their source. Maybe use that in the future for such things.

For now, if you're app forks GPL code, you have to release the source, pull it, or hope nobody cares. Good to start noticing these little, but important, things early to develop good habits.