Trivia: In this season, you can see DJ, Gibler, and Stephanie having a conversation in the garage. Before the renovation, Stephanie expressed her concern about there being a monster in the garage. However, in the episode before this, they renovated the garage and turned it into Joey's room. The episodes were aired out of order, hence the discontinuity, but it's not strictly a "mistake", more just an indication that this episode is clearly set earlier in the season.
Suggested correction: The episodes were simply aired out of the order in which they were produced.
In the "world" of the show, however, this is a mistake. The garage can't be renovated in one episode, then be the former garage in the next episode. The rules of this site note that behind-the-scenes explanations are not valid corrections.
No. The correction is valid. It's not a "behind the scene" explanation. The show's continuity remains constant if you watch the episodes in the order they were produced. A network's decision to air them out of order is not the fault of the show. This would be like if you had a book on CD where each track is a chapter but you played the CD on shuffle and then blamed the book for its continuity issues.
I can see both sides of it in terms of it being a "mistake", but it's such a grey area that stuff like this is rarely worth a debate. It's such a blatant discontinuity that it's a byproduct of the episodes being shuffled, making this more of a "prequel" rather than it being a mistake. A bit like errors in subtitles, it comes down to what strictly counts as a mistake in the show vs. A problem arising after the fact, whether someone's "at fault" or similar. I'll refile this as trivia.