You should also look at this as % of merchants and users in the world.

Is it 10%,50%,or 0.001%?

What percentage of merchants and users accept HKD?

100% in Hongkong, which is also where the most HKD are circulated.

Pointless comment. Bitcoin is a borderless technology. There will never be, by design, a "Hong Kong-sized" area with BTC accepted everywhere. That is, unless BTC achieves world domination :-)

OP asked "in the world"

If BTC was circulated in only a Hongkong-sized area, that would be a fair comment. It isn't, the area of its circulation is the world.

Or hamburgers? After all, you can trade them for the local currency. Hamburgers must be a currency!