Is this really true (I just watched the video, so still learning these concepts, so please be kind)?

The linked video makes a clear distinction that OT and CRDT are different, as OT has the idea of a centralised coordinator to ensure consistency by mutating the proposed, conflicting operations whereas CRDT uses commutativity to attempt to make conflicting operations an inaccessible state

There is no formal distinction between an OT and CRDT algorithm.

It's true that the most popular OT systems have a central server -- but there exist OT algorithms without a central server.

It's also true that CRDT algorithms tend to require too much memory usage to be practical -- but there exist CRDT algorithms with bounded memory.

There are even algorithms that can be equally called OT and CRDT.

No, CRDTs and Operational Transforms are not the same at all.

Well, so OT is the same as CRDT except that you also have a centralised server that decides the merge conflicts.

Not true whatsoever.

Actually, the algorithms have a lot of overlap. The original CRDT (called WOOT, for "WithOut Operational Transform") was derived from an OT algorithm.

Historically, what happened was that the OT research community couldn't solve consistency without adding tombstones into their data structures that recorded deletions (and generally kept these deletion marks around forever). They called these "tombstones." People didn't like that you had to keep them around forever, but they seemed to solve the problem.

Over time, some researchers decided to just keep more things around forever, and promoted the idea that you don't need to do as much transforming of operations if you just preserved all operations in a spatial data structure, not just the tombstones, but everything. They came up with a new name this style: CRDT.

But in fact, the technical definition of a CRDT actually fits OT algorithms quite well. A CRDT just means that you can accept any operation at any time. That's what a good OT system also needs to do. So there isn't a technical distinction between an OT or a CRDT. They each define a set of features, and your synchronizer can possess OT features, and it can possess CRDT features.