I ran into this exact situation once when I was a Night Manager. Upon seeing what happened, I went into "service recovery" mode. The guest stopped me, saying he was just asking for help in placing the bed board under the mattress.

I got on the radio and called for some help. The guy that came just happened to be the one who put the bed board there in the first place. He apologized directly to the guest, admitting that he had never seen a bed board before. He also explained that in the area of the country where he grew up, virtually everyone slept on the floor or a similar hard surface.

Thankfully, the guest had no xenophobic tendencies. He said that he was baffled as to why the bed board was just under the sheets. But, after hearing the explanation, it made perfect sense to him.