The text section of an executable is the actual executable code, this is what it refers to. On Linux this request is ignored, it is just an optimisation, made by the admin. The kernel can do this for it self, without the prompt.
It is saying that if the executable text gets swapped out, and the process ends, then keep it for next time. On linux (local)executables are not swapped out, as it is as quick to reload from file. Maybe it is a bit different for NFS.
The sticky bit has other meanings for other file types:
You described for executables.
For directories, it stops non owners from deleting files.
I assume that nfs is the same, when I used it 20 years ago it was.
Later, on SunOS 4, the sticky bit got an additional meaning for files
that had the bit set and were not executable: read and write operations
from and to those files would go directly to the disk and bypass the
buffer cache. This was typically used on swap files for NFS clients on
an NFS server, so that swap I/O generated by the clients on the servers
would not evict useful data from the server's buffer cache.