Frankly, tanks are probably the worst to explain any fight mechanics because they are usually dealing with different things from the rest of the party. Attacks that only the tank has to deal with and ensuring defensive cooldowns are done at appropriate times, tank swapping, boss positioning, etc. Healers see all of the flow of the fight and probably need to be the best informed overall.

That said, the person who should explain a fight to a newcomer is the one who a) knows the fight and b) is capable of clearly describing it. Just being the tank does not necessarily qualify you.

And, to support the OP, if you are in a party and think someone is not doing a good job at explaining things, then step in and make the corrections - or - STFU.