Revealing my ignorance on this topic: Why would IBM care who owns their stocks, assuming the specific shareholder doesn't try to take influence on the development/direction of the company?
Because of the herd mentality around investing who invests in you does matter, but not for this discussion.
I was thinking more along the lines of Buffet talked with people at IBM and realised that he understood the way they operated.
It is in the realm of possibility (and quite likely) that he talked with people inside IBM. But I don't think they were really pushing for him to buy it. At least it doesn't appear that way.
[1]http://tech.fortune.cnn.com/2011/11/14/warren-buffett-ibm/
He would read company reports, even if he had no plans to invest. It is one of his hobbies (not only a job).