This dream is apparently a flashback, to shortly after issue #96. The old X-Men appear and fight with the new X-Men. Which we saw in #100. Since this is set before that it only makes them look stupider in #100 for failing to immediately recognise that they were impostors. Rather than the
holodeckdanger room malfunctioning or it being robots, it's instead Xavier's dark side gone wrong, and intriguing hint at what will become Onslaught.
What's going on here? Well, the clue is in the pencilling credit: Dave Cockrum and Bob Brown. It's a fill-in issue, originally created as inventory in case of this eventuality, but in a really momentum-draining position. And the title was bi-monthly at this point. Ouch.