According to the information here, it sounds like the creators both collaborated with The Nicaraguan Sign Language Project when designing the game, and give all proceeds from the physical edition to them too - having raised over $15,000 so far. (Quote below for ease of reference.)
So it really seems like they've made a solid effort to avoid the things raised as hypothetical issues above - and it makes sense that they wouldn't consult ASL users in Bay Area for a game related to the formation of a linguistically unrelated sign language from Nicaragua, especially when they had consultants from the NSL community.
"All publisher proceed from the physical version go to support sign language education in Nicaragua, currently The Nicaraguan Sign Language Projects (NSLP). This has raised more than $15,000 in donation to date. Thorny Games thanks the NSLP for their guidance and input on game design."