The Wikipedia article[1] cites a few sources which support “Think Different” as a reference to IBM’s “Think”. But IBM was one of Apple’s biggest business partners at the time, as part of the AIM alliance[2].
While AIM could be seen as a failure—PowerPC never threatened x86’s dominance—its legacy, RISC, later became ubiquitous with the shift to mobile via ARM.
You are correct: 1985 vs 1991. My bad. I just heard about AIM at the time, whereas ARM was relatively unknown (well, at least to me ;) until the rise of mobile.
Edit: It’s a bit confusing because ARM the architecture is older than ARM the company. But yes, both precede AIM/PowerPC.
My main point was that mobile made RISC ubiquitous.
If you consider the evolution IBM 801 -> ROMP -> POWER -> PowerPC then you might say the that the roots of the PowerPC are from 1975, or 1982, or 1990 or 1991 and you would have a valid point in all cases.
But it is very reasonable to consider ARM older than PowerPC.
1: https://en.m.wikipedia.org/wiki/Think_different
2: https://en.m.wikipedia.org/wiki/AIM_alliance