Marvel Studios has never addressed it. Since Spider-Man: Homecoming and the MCU are both under creative control of Marvel Studios, they should have the final say in what connections are and aren't canon. For example, the post-credits scene for Venom: Let There Be Carnage was done in collaboration with Sony.
Also, it just doesn't make any sense. Why would Strange's spell send Toomes to a universe that isn't his own when the entire purpose of the spell was to send the reformed villains home? Plus, how would he know it has to do with Spider-Man?
