No idea whether Notion uses CRDTs, but last writer wins is a (naive) strategy for editing text. You can see this in the article — if you edit the LWW Map, for example, even though the keys are merged, each value will be taken from one peer or the other. Once you get to that last “primitive” CRDT — the register holding each map value — updates are atomic. So Notion may be using CRDTs for e.g. the order of blocks in a page, but not (yet?) using them to merge text.