If it is a DDOS attack then why can i log in the NA server fine? Why does everything work fine till i start a game and get infinite firewall errors?
Champion select doesn't happen on the same machine as the game itself. If the attack targets the game servers, you won't see anything bad in the queue or during champion select, but either the game will fail to launch or you will get a message about being unable to connect to the game server.
DDoS isn't the only thing that causes this error, by the way. You can also get that firewall error message your ISP's routing table has a different path for the game server than for the host server, and that path runs over an oversaturated network node. Typically this failure mode happens during peak Netflix hours.
WHY CAN I PLAY IN ANY OTHER SERVER IF LOL IS GETTING DDOSED
I am not aware of any attacker ever trying to hit all ~40 LoL server farms at once; almost every ddos attack has been limited to a single region. Most ddos attacks are even more specific than this, targeting a particular type of game service. Going to the extreme end of this, we had attacks like LoLDrop that targeted a single machine, the one that happened to be hosting the game of an individual player the attacker wanted to mess with.
Anyway, you shouldn't expect any attacker to be able to kill LoL globally. Instead, attacks try to deny particular services, typically in a single region. For example, this week we had a big attack aimed at the NA login servers, which resulted in hilarious login queues but nothing bad on the game servers, so those already logged in could play ranked just fine. Meanwhile, LAN has been smooth as silk all week.