Oh, you CAN do many to one if you want, but he meant that if you do, you might run into problems.
He meant that a 301 is intended for an URL that has _moved_. It isn't logical to _move_ a bunch of URLs to 1 place.
Say you used to have your contact page here: example.com/contactus but for some reason you decided to move it over here: example.com/howtocontactus, so, you 301 the old URL into the new URL.
The point is that probably a 404 or a 410 is better suited for the situation of many urls that no longer exist.
Meaning, if the URL:
- no longer exists -> use a 404 or 410
- has simply moved to a new URL -> use a 301
If the URLs are dead, kill them off with a 404 or 410. If they have moved (which will likely be a 1:1 mapping), 301 them.
If you 301 a bunch of URLs into one destinaton URL, you will likely have problems.