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!