first off, that video was made BEFORE burning crusade. the guy is level 60, mostly in BWL gear (mantle of the blackwing cabal, ringo's blizzard boots, t2 gloves, mish'undare from what i can tell). he had a pom/frost build (21/0/30).
then it was actually something to get a 5k crit. at 70 in decent gear and with the right spec, it's not really a big achievement.
also, resilience was not in the game at the time this video was made. hp numbers were much lower (hence the many one-hits).
important: stacking two burst damage trinkets at the same time is no longer possible, so the macro is largely useless.
secondly, quoting your largest crits says little about your overall damage output, especially against mobs with damage debuffs or vulnerabilities (like bog striders in SSC, first mecha boss, curator, magtheridon while banished, even the drakonids in BWL). in this vid it's pvp which would mean little to no pots, buffs, debuffs.
in a raid setting with a fire spec and around 1k spd, you do 7k+ crits including ignite if the target is below 20%.
thirdly, buffs that reduce cast-time (like pom) or increase crit chance (like moonkin aura) will NOT make your crits bigger. just faster or more of them. it will obviously increase your dps, though. don't mix up the maths. he frosts his targets to increase his crit chance, NOT his damage.
getting your biggest ever crits, pulling aggro and dieing or causing a wipe doesn't make you a good mage, because once dead, you do zero damage.