That's a very poorly worded reply.
But I guess what he meant was RTP is theoretical and doesnt account for 'lucky' or 'unlucky' streaks.
Casinos and slot providers have no reasons to be rigged if they can be clean. It is legal 'robbery'. The house always win, no need to rigged a unfair system.
However there are illegal or bad casinos, so play and trust those vetted.