As I recall that scene starts with a big time marker for 2007, which we can note is never the case for any of the other scenes where drugs make us question the canonicity, and there’s nothing unnatural happening visually to indicate that it’s due to a trip, like the anomalies in Cuddlywhiskers’ room and >!Time’s Arrow!< (which are generally believed to be flashbacks of real events with slight alterations) or in >!The Showstopper and The View From Halfway Down.!< (where the scenes in question take place entirely within Bojack’s mind and only have canon significance in that scope)

Now Downer Ending throws a bit of a wrench into this because it does have meta bits with time cards being wrong and things being fabricated without visual indicators, but both of these things are very clearly communicated to be falsified, with the time card in particular being clarified by a second time card. Of course the whole show is made up, it’s fiction, so anything could be true, but I find it much easier to believe that what’s being communicated is that all of that scene did literally happen.