That is indeed the problem.
At the moment, the FreeBSD linux emulation layer is a bit out-of-date (Fedora Core 10), so it cannot run Steam since it requires some of the newer (Ubuntu?) libraries. There is currently a push to try and update the linux compatibility layer in FreeBSD, but I am not sure what the current status on that is.
On the plus side, if you install Steam through Wine it actually works quite well... :-)
~ Ken Moore ~