If you're ok with giving your fish just enough water for them to be ok in, rather than given them a bit more then it is indeed true.
With all the people that keep and recommend keeping fish such as Oscars in 50 and 55 gallon tanks, I don't see how keeping 1 fish that will grow to no more than 3" in a 10 gallon tank is
just enough water for them to be ok in.
However, being able to keep 1 f8 per 10G doesnt mean you can keep 1 in a 10G.
Both PufferPunk and RTR have said 1 F8 per 10G
and that 1 F8 would be perfectly fine in a 10G.
As for keeping water parameters stable in a 10 gallon, I
definitely agree that it will be more difficult than in a smaller tank. I have the utmost confidence that I can keep the tank in good condition for the F8. However I wouldn't recommend to someone new to the hobby to attempt to keep a 10 gallon in good condition for a fish as sensitive as a puffer.
So, back to the original question by Paintballfan, if your friend has been keeping fish for a long time and has plenty of experience keeping good water quality in his fish tanks over a long period of time then he may be ok with the F8 in a 10G. However, if he is not experienced in the hobby or if this is his first tank/fish then this is a really bad idea. B)