That's correct... and just to reiterate what laogui32 said:

In this situation, Ross is being negative about a positive situation.  Instead of seeing the free ticket as a positive thing, he is sarcastically accusing Chandler and Joey of not being able to agree who got to bring a date.  Therefore, he is viewing the "free ticket" as a glass half empty (negative), rather than glass half full (positive).

What does the phrase "The glass is half empty." on the last line

(Chandler and Joey enter. Joey is counting his steps.)
Joey: ...Ninety-five, ninety-six, ninety-seven. See, I told you! Less than a hundred steps from our place to here.
Chandler: You got waaaay too much free time.
Joey: (to Ross) Hey! Here's the birthday boy! Ross, check it out: hockey tickets, Rangers-Penguins, tonight at the Garden, and we're taking you.
Chandler: Happy birthday, pal!
Joey: We love you, man. (Kisses Ross)
Ross: Funny, my birthday was seven months ago.
Joey: So?
Ross: So, I'm guessing you had an extra ticket and couldn't decide which one of you got to bring a date?
Chandler: Well, aren't we Mr. "The glass is half empty."

It refers to personality type - positive/optimistic or negative/pessimistic
'Are you the type of person who given a glass filled halfway up, says:

A. The glass is half full (optimistic) or

B. The glass is half empty' 

Chandler is suggesting Ross is 'the pessimistic kind'