You were way ahead of me on this one! But yeah, that is usually my concern, newbies seeing the post and thinking scratch is okay.This was absolutely a concern of mine.
Their primary food is still crumble (the humidity's gone, so I'm leaving that feeder in for now) and foraged pellets. The particular whole grain mix I got has tiny little vitamin/mineral pellets. In a regular feeder, the birds would eat around this and pick their favorite pieces.
But my poppy peck toys are suspended over stepping stones. Each piece that falls is considered high value, and the birds scramble to chomp it down. Vitamin/mineral pellets included. The stone also lets me monitor and see if they do start to ignore the premix pellets (in which case, I would discontinue this style of feed.)
I appreciate you bringing attention to this though! I don't always consider that someone might emulate what I'm doing without understanding the risks.