Yep, the Beatle was tripping balls. Specifically, he had just taken a hit of DMT with famed 1960s art dealer Robert "Groovy Bob" Fraser. From the NME quoting a paywalled Sunday Times interview:
"We were immediately nailed to the sofa… And I saw God, this amazing towering thing, and I was humbled. And what I'm saying is, that moment didn't turn my life around, but it was a clue.
"It was huge. A massive wall that I couldn't see the top of, and I was at the bottom.
"And anybody else would say it's just the drug, the hallucination, but both Robert and I were like, 'Did you see that?' We felt we had seen a higher thing."
Illustration: Mitch O'Connell's fantastic Paul McCartney poster art.