That is not a non-locking mechanism. It just hands off the locking to the kernel which locks the directory when it reads from it or writes to it. It has the advantage of the kernel locking implementation being very well tested.
Of course, errors might not all have such nice, unique, numeric identifiers so the files might have to be named more like "ERROR.Error inserting record into table WIDGET, unique key violation on column UPC". And even that won't work if the comparison for "same error" isn't easily reduced to "string equality".
But, most importantly, your solution (as described) has a race condition between stat and creating a file. You can probably fix that a couple of different ways.