This was a very busy period in the history of computer networking, and many things happened at the same time, which can make it hard to make any statements about "x is based on y." The OSI model is most definitely not based on TCP/IP or vice versa. While TCP/IP was generally an earlier effort there were revisions being made to TCP/IP at the same time that the OSI model was being designed, and TCP/IP did not become the clear leader in computer networking until after the completion of the OSI work (arguably not until as late as the mid-'90s depending on how you feel about the issue of "WANs" vs "LANs" which often took different paths in the '80s). For most purposes they were parallel efforts, and the designers of the two were each aware of the other but mostly working off of different prior art.

This further makes the point that many of the differences between TCP/IP and the OSI model were very intentional choices, as the OSI designers were well aware of IP and viewed it as unsuitable while the adopters of IP were judging the OSI model to be impractical.

The article doesn't say that OSI was created before TCP/IP. It says that X.25 was created before TCP/IP, and that OSI is an abstraction of that particular design (and thus doesn't map neatly to the IP stack).