Keep in mind that a young nonverbal kid is very hard to assess accurately for things that aren't readily observable, such as cognition or receptive language. It's even harder if they're autistic, too. If they fail to respond, is it because they:
a) didn't understand the instructions (receptive)
b) didn't understand the concept (cognitive)
c) couldn't get their body to do what they wanted it to
d) didn't see the point of doing what the adult wanted from them, or didn't want to do it for whatever reason
e) were too overloaded by some sensory issue to pay attention to the questions or give the right response
f) were too scared of an unfamiliar situation or an unfamiliar person to pay attention or give the right response
g) some other reason
I have heard many stories of kids who scored way lower than their true abilities on a cognitive or receptive language test. It's possible the results could be accurate, but with a nonverbal 16 month old with suspected autism, a receptive language test could very easily end up underestimating them.