Seems like a mistake. That’s an ordinary TGV they probably programmed wrongly in the databases.

Reservation free IC routes Lille-Brussels go via Kortrijk/Courtrai or Tournai.

Yes I know about the "usual" routes without TGV, that's why I was stunned to see this one.

Figured out that it's likely a messed up entry in DB's system. There's a Eurostar with same departure and train number. Too bad.

The rail planners of Interrail/Eurail also had some issues with this lately. Some bad entries in the underlying MERITS system are probably the cause, if DB has this too.

NS International also show this train Brussels-Lille so it looks very much like a data problem in MERITS. Maybe it will be solved by the Friday (early) morning update.