>>> no other species could be kept with them
That's an odd thing to say, unless there was another reason for saying it. If your tank is large enough to hold them, most loaches will live with each other.
The point may have been that most loaches grow quite large, and should be kept in groups of 3 or more. Clown Loaches easily reach 8"/200mm and in good conditions will grow much larger. So we are talking about 3 large fish here. Many of the other Botia species also grow quite large, although you'll hear claims that they don't.
If your tank is large enough, and you avoid the aggressive species, (modesta, hymenophysa, morleti, etc.), they should be fine.