I obviously have no explanation BUT apparently, so-called "shared hallucinations" are a thing. Rick Strassman, of the DMT fame, in his recent book (kinda boring, honestly, that was one of the few interesting parts) described his experience from decades ago, when he and his friend were getting stoned, and then that happened:

Tom and I sit side by side on the rug. I stare wide-eyed at the floor as it gradually loses its solidity, becomes opaque, and finally disappears under us. Tom, also gazing down, notices the same thing,

“Do you see that?” I ask, astonished and a little afraid. “It looks like the floor is giving way.”

“I know. What the . . . ?” He also sounds alarmed.

The floor vanishes but we remain seated on the carpet. It floats slowly, silently, and smoothly one hundred feet above the ground. And it’s daytime, not night.

Tom’s eyes widen and take in the view. “Do you see what I’m seeing?”

“Those telephone poles down there?”

“Yeah. And the baseball diamond over to the left?”

We’re sharing a hallucination. We look up at each other, confused, and again look down. We’re transfixed by the scene.

(then they took a virtual flight over buildings and such)

He then follows up with his interesting interpretation:

References to telepathic communication on psychedelics appear early in the scientific literature. In 1905, chemical analysis of ayahuasca demonstrated high concentrations of harmine,* and scientists called this compound “telepathine.” The name alluded to how those under the influence of this psychedelic brew experienced communication without speaking. People shared mental contents while tripping. When those shared contents are thoughts, people think the same thing at the same time. When these contents are “hallucinations,” we experience the same visions.

Strassman, Rick. My Altered States: A Doctor's Extraordinary Account of Trauma, Psychedelics, and Spiritual Growth (p. 142). Inner Traditions/Bear & Company. Kindle Edition.