The other sites are wrong, or you misread the information. Torterra's minimum HP at lv100 is 300, as shown here: http://pokemondb.net/pokedex/torterra
It looks like you have quite a low HP IV. Actually it must be 12, if you didn't train any EVs in HP since natures don't affect HP.
And for Swampert, his minimum is 310. So yours is pretty good in that regard.