The first paragraph I find under Key Features is:
Distributed Transactions: TiDB uses a two-phase commit protocol to ensure ACID compliance, providing strong consistency. Transactions span multiple nodes, and TiDB's distributed nature ensures data correctness even in the presence of network partitions or node failures.
It claims to ensure correctness in the presence of partitions, not availability, so I don't think that's a claim that CAP is wrong? I would expect it to be unavailable if it can't provide a consistent response.
I don't know about memory management. It seems go may not be used for the storage layer, but in any case, it wouldn't be the first attempt at a DB on a garbage collected runtime. I can think of at least Cassandra on the jvm and CockroachDB also on Go. I do prefer that DBs do their own memory management (as well as storage) but this is not as unique as it used to be though.