no elo no rank and all is different

What are the real metrics and why is rank not elo?

There are 3 terms - RATING, RANK, and LEVEL, my understanding of them is as follows...
(apologies if this is inaccurate, someone with more expertise can correct my post)

RATING
ELO and WHR are both ratings systems to calculate relative skill between players.
Zero-K uses WHR as the player rating system, calling it ELO is technically incorrect, but ELO is a more widely understood term.
This metric is used for balancing.

RANK
Ranks are used to group players by rating, into ranges.
The RANK determines the colour of your LEVEL.

This is a cosmetic indicator of a players skill/ability.

LEVEL
Level is a proxy for playtime, more you play more you will level up.
It has nothing todo with rating or rank and only shows how experienced (in game time) a player is.

About rank icons.

I'd say, the color of the icon is the rating, while the shape is the level.

It's actually annoying that I appear silver (and blue soon if I play lobsterpot a couple more games) when my matchmaking skill is yellow. Would be interesting if these two are separately shown :D