In the DMVs, you are looking at just portions of memory usage and also looking for memory change notifications with the ring buffer query.

Max server memory doesn't fully control or account for all of the memory used by an instance. Max memory controls buffer pool, caches, lock manager, compile memory and CLR memory. These are tracked by the different memory clerks.
Memory for thread stacks, memory heaps, non-SQL Server linked server providers and other non-SQL Server dlls are not part of the max server memory.

It not at all unusual to see the totally memory usage by a SQL Server instance be higher than the max memory setting.

Sue