Suspicious ADSL: router single account with two different password

With Router provided by my ISP - today I was playing around with it. Tried to login the router via ssh.(admin/mypass1) then I saw some shell commands & one of them is 'show login':

ADSL Router#show login
Useame Password Priority
admin mypass1 2
user dump 0
admin diffpass2 1

I wonder why 'admin' has two passwords? I tried to 'ssh' with diffpass2. It worked too! Is that normal?