Quoting myself for great justice.
If you want to get technical, then no. They do not give a definitive picture of the skill level of a player. However, in that case neither does actually playing a match against said player. After all, they might be having a bad day. Or several bad days. If you want to get this specific, the only thing that 'means' something is playing someone in countless matches on every single map, with every possible amount of teammates, to even out the factors of luck, favourite/least favourite maps, bad days on either side, bad servers, bugs, etc.
Also, assuming they're not gaining their K/D in 'joke' matches and they're actually getting away tank camping enemies of their own skill level, I'd say they are indeed better. (Given that the game doesn't enable obvious exploits, which it doesn't.)
If that's what wins them matches, that's what you'll be beaten by if you play them. Some tactics are not as 'honorable' or pr0 as others, yet they still work for some players.
To reiterate: Stats mean something as long as you compare several of them with players of your own gametype. There might be slight differences between a ctf/instaTDM player and a ctf/duel player of equal skill, but -omitting the obvious statpadders, as everyone with a brain is capable of- a couple of their stats combined give a pretty good picture of a player's skill level.
