They have to mean 5g, as does the guy who responded to you who seems to have made the same mistake. The recommended dose on most creatine containers is around 5 grams. 5mg is so little that it would be impossible to measure without a mg scale.
The last sentence there is an impressively neat tautology. I love it
I always wondered why I couldn’t measure mg with my gram scale! I just kept asking myself where are the sig figs?
To your snark, I was meaning to convey that a standard kitchen scale wouldn't be accurate enough to measure 5mg, necessitating what is typically referred to as a precision or mg scale.