that’s not accurate. as the excellent new manual states:
xmp files are read in the beginning and always synced as you go (kinda write only). for better access the data in the sqlite db takes precedence. if you want to alter the xmp from the outside (write new tags from digikam or whatnot), dt can be instructed to launch a crawler on startup to ingest the new changes (also see the docs i linked above).
hth