The pipe in the second block turned your regex into one that will match any string, including Joe Blow, Amelia Earhardt and Barack Obama. With the trailing pipe, your code now says: Match tom jones, or greg herman, or... whatever. So whatever matches.
The problem with the regex in the first block is that you're using the x modifier, something you appear to have forgotten when you wrote tom jones and greg herman. Note the space in between the first and last names - Perl is ignoring it. That regex will in fact match the string tomjones and gregherman. To make it work the way you want it to, you have to say tom\sjones | greg\sherman.
Hope this helps!