Strictly speaking "paradox" means something that is both true and not true. Since that is clearly impossible, it is more common to talk about an "apparent" paradox, as done here- something that looks like it can't be true but is.

Actually, I wouldn't consider this to be at all paradoxical because you can treat it as .10+ 0.0010+ .000010+ ... using blocks oftwodigits at a time.

.10+ .0010+ .000010+ ...= .10+ (.10)^2+ (.01)^3+ .... which is a geometric series with "common factor" .10. Do you know the formula for the sum of a geometric series?