Actually you can use skills while blocking and it can continue blocking, weird thing. It costs roughly 200 stamina or something per attack to block. For that long blocking, either using potions or has a good regen and a good stamina pool.
Getting hit while blocking lowers your stamina. You cannot block forever.
Have you never ran with 1H/Shield before in ESO? It's costs a hell of a lot of Stamina to interrupt attackers. Now if I just want to hold my shield up that costs nothing but I also can't use any abilities while I'm blocking. If ZoS adds a Stamina drain just by holding the shield up that'd seriously effect actual tanking in PvE. They might want to look at seeing how they can balance it ONLY for PvP. There are some MMO's that XYZ ability has different effects against players than it does against NPC's.
The guy just blocked and bashed all to death
I find your story hard to believe as well; blocking attacks DOES cost stamina; although there are passives to reduce the amount of stamina it costs, there is always a stamina cost left.
furthermore, he managed to keep 5 players in front of him? what did the attackers do, twiddle their thumbs and use emotes? That doesn't necessarily sound like tactical play by the blocker, but like inept play of your allies, especially since blocking impairs movement speed, pretty sure even with the combat movement passive (not sure if that one even works now) so you should really be able to get behind him.
1h + shield is meant to be a tanking spec so he should be able to withstand a lot of punishment from the players surrounding him, but him killing all of you of is more than likely your own fault and (I'm sorry to say) a l2p issue.