Welcome to Yorkie Talk! You and Foofy will learn lots from this site!
I keep the hair on my babies "stubbies" trimmed a little shorter than their body hair just because I love the way it looks. I love to see their little stubs wagging at the speed of light!

( a happy yorkie tail- is there anything cuter??

)
Maybe his previous owner trimmed the hair on his tail and that is why it is shorter? I am sure that in time it will grow out some. Some yorkies puppies have a body full of hair that will not quit, others take their sweet time growing their adult coats.
Would love to see some pictures if you have any!