1) The episode doesn't contain "Q" in the title.
Neither did "Encounter at Farpoint," "All Good Things...," or "Death Wish." Only 2/3 of the episodes featuring Q had "Q" in the title.
2) No one but Picard saw Q.
The same goes for "All Good Things...".
3) I don't recall Q ever mentioning the events of the episode in his later appearances.
The same goes for "True Q" and "All Good Things...".
The most you can legitimately say about "Tapestry" from these points is that it might not have really happened. It can't be conclusively proven that it did, but neither can it be conclusively proven that it didn't. Absence of evidence is not evidence of absence.