This was introduced with Mp3tag v2.87c
CHG: importing tags via Discogs tag source supports track numbers and disc numbers from Discogs. (#19744)
Previously, the Discogs tag source simply enumerated the tracks, making it impossible to import the actual track- and discnumbers from Discogs.
As a side-effect, tracknumbers from Vinyl releases are now imported differently. If you prefer normal tracknumbers, you can revert back to the previous Discogs tag source or use the auto-numbering wizard via Ctrl + K or some of the other suggestions from this topic to adjust the numbering.