Not everyone agrees:

https://www.gnu.org/philosophy/open-source-misses-the-point.en.html

In practice, open source stands for criteria a little looser than those of free software. As far as we know, all existing released free software source code would qualify as open source. Nearly all open source software is free software, but there are exceptions.

First, some open source licenses are too restrictive, so they do not qualify as free licenses. For example, Open Watcom is nonfree because its license does not allow making a modified version and using it privately. Fortunately, few programs use such licenses.