Hello 5359!
Great catch! Those tags must have come over from QGIS when the public source data was split into smaller manageable chunks. The ID tag is simply a sequential number for each file/chunk, and the size tag indicates the number of elements (ways) contained.

I’ve now closed changeset osm.org/changeset/173069695 to remove them, and I’ll be extra careful going forward. Thanks again for pointing that out!