That comment was a rhetorical oversimplification (typewriters to computers) meant to encompass not just the 1980/90's transition into software and systems consulting but also a much earlier transition from mechanical office equipment and punch card machines and tabulating equipment to being one of the early vendors of mainframe computers (in the 60's).
IBM wasn't always a computer company. It was started in the 1910's as a consolidated company for all manner of mechanical equipment - tabulating and punch card machines (used with mechanical tabulating equipment - not computers) to be sure, but also meat grinders and scales. By the 1930's they were selling typewriters as well.
In the 1960's there was a massive restructuring and redirection as the company became increasing concerned that its mechanical tabulating equipment was going to be overshadowed by the newer electronic computing equipment. Although they had been involved in electronic computer long before that, it was not the their core business until after the 1960's restructuring.
For those outside of the computing world, IBM's reputation in the 70's and 80's came from its selectric typewriter. According to Wikipedia, at its peak the IBM selectric had a whopping 75% of the typewriter market.
I think we take IBM's involvement in computers so for granted these days that we fail to realize that it had to make a major internal strategic transition to get there. Not every company has been so successful even when they created the opportunity in their own backyard. Xerox muddled around with the software and operating system that eventually became the Mac PC because, even though image production (the Xerox copier) was a core product line, it just couldn't see the market for a personal computer with pretty pictures and a mouse. According to the book I read on the history of their research park, they weren't even all that sure there was much of a market for a personal computer. They also feared it would distract attention from other product lines that were important to them at the time.
As for IBM, by encouraging the mainframe business they killed off their mechanical tabulating business. By being early vendors of the personal computer they killed off their typewriter business and the typewriter market as a whole. Two core product lines from the 1940's - gone. It may be an oversimplication but as a summary of IBM's history of reinvention, I don't think "typewriters to computers" is all that wrong.