I'd put the percentage even higher. There are exceptions like your grandson (was it just therapy or did he need drugs), but autism and "non-verbal" are the new excuses of the last 20 years. BTW, a toddler not talking doesn't mean anything. As I recall, Einstein's parents worried because he didn't start speaking until he was 3. Sometimes there isn't enough to interest a kid.
One of my best friends growing up would have been diagnosed with ADHD and drugged up to hell. I'd have been called OCD for wanting to arrange things in perfectly straight lines, which is supposedly an indicator of being on the "spectrum" (God I hate that term), but that was simply the game I played and wound up playing alone, because other pre-schoolers left messes everywhere.