Ten years , not twenty. Bhuka are Venerable at 49 and get a maximum of 2d10 years on top of that.

Half-orcs are Venerable at 60 and get a maximum of 2d10 years on top of that.

so- on average, a Bhuka will live around 11 years less than another goblinoid.

Still a big gap- but maybe deserts are less forgiving and shorten their lifespans?

Races of Faerun was written several years before- and is a world-specific book- so it's possible the Sandstorm writer hadn't read that.