Of course it's not the largest prime that exists, does this really need to be explained. It's the largest prime we have found so far, that's it.
There are infinitely many prime numbers, infinitely many odd numbers, and infinitively many even numbers.
There is a million dollar reward for anyone that can prove primes do stretch to infinity or if there is a largest one that ends them all. At the
moment, having super computers looking for them is the only way to help prove it, but still leaves some doubt as infinity cannot be reached through
computational means.
Why this is important is because the global financial system is built on the security of the difficulty in factorizing primes. If a short cut does
exist then it opens to door to a complete financial meltdown at worst, or massive financial corruption from those with the knowledge at best.