Normally I would also have said it sounds like different men, but looking at the original register entries (available on Ancestry) I would agree the signatures look very similar and the inclusion of a common witness is compelling evidence to suggest he is marrying twice.
The key thing is that on the 2nd marriage he claims to be a bachelor, which cannot be true, he has to be either a widower or divorced (unlikely but possible).
I would be looking for what happened to his first wife Catherine - did she die (probably not, or he would have been shown as a widower), did she marry again and can she be found in later census records. Were there children of the first marriage - what happened to them ?
It appears to be a potentially bigamous marriage , which isn't that uncommon.