I thought that the case also. However comparing them side by side they do not appear the same. The Polar Express couplers seem a little bit taller by a mm or two. Also, I failed to mention the caboose I purchased will not stay coupled to the other cars with the Lionel couplers. I thought they would work no problem. But I haven't really determined the root cause as to why the caboose is coming uncoupled.
Thanks!