From what I can work out (via a quick google) the GLC is a part of the WPPSI calculated from two optional subtests. Those subtests sound very like the Vocab test.
I, too, am not terribly familiar with the WPPSI but, if GLC is essentially the vocab part of the test, I'd be cautious at this point and have him retested on the WISC or SB-V later.
I say that for two reasons:
1) vocab is one of the more heavily g loaded subtests, meaning that it is a good indicator of giftedness not just processing skills like memory. This might lean toward the assumption that giftedness is part of the picture. Whether 2e is as well I'd probably be unsure at this point without more data.
2) vocab is also one of the subtests that is less stable and prone to artificial inflation and deflation early on due to environmental influences, thus I'd be less likely to rely on it being a truly highly gifted number at his age. The same score (99.9th) at 8 or 9 would make me look harder at the child having a huge span btwn subtests and that indicating a concern such as 2e.
Wait and see is a cruddy place to be, but I'd probably do that for now unless school is really becoming a major problem.
