You are right of course. I meant to say that it's "...around 25% of "Desktop/Laptop Visits" (where Mobile Device Type ≠ Other)". Thanks for catching my mistake.
It's still large for us too. On many of our sites, the "Unknown generic android mobile' still hovers around 10% of All Visits and around 25% of "Desktop/Laptop Visits" (where Mobile Device Type=Other).