It’s a strange diagram but shows what you have to know. If you ever seen different keyed m.2 cards, you should understand this. The important thing is the location of the keys, the notch. All m.2 cards has an ‘up’ and ‘down’ side, it shows only the ‘up’ side. You have to look inside the receptor to see the pins, that’s why it shows both sides, it’s not possible to see one side only on the receptor as they are in a plastic casing. Usually you can’t see the pins on the mobo, only the key.

You can see a similar diagram on wikipedia, both sides of receptor, top side if card:

https://upload.wikimedia.org/wikipedia/commons/thumb/e/ed/M2_Edge_Connector_Keying.svg/560px-M2_Edge_Connector_Keying.svg.png

The offset you were writing about doesn’t matter, iz actually helps. You can’t accidentally insert the card upside down. The location of notches also help with this, as not all possible notches used yet, but in the future it could change.

These connectors are really small. The receptor is similar how sodimm connector works, but smaller. Are you also afraid about inserting a ram in an laptop? It’s basically the same.

Read more about the connector in wikipedia, I’m really happy this slowly replaces sata, msata, mpcie and even pcie in current pcs.

en.wikipedia.org/wiki/M.2