Weel, yeah....I'm sure it is bullshit. Papers at that time carried all sorts of "interesting" stories. The truth wasn't exactly their first priority.
The story in question was "believable" at the time for a few reasons though.
1) The Arizona Territory was little explored at the time.
2) SE Arizona hosts many very "odd" creatures. For many primarily South American species, it is at the northern-most end of their range. For example, a person from say Ohio, would be shocked an puzzled by the appearance of the native Coatimundi. Likewise, the sight of a Jaguar would be quite odd to many people.
3) People were not that educated back then.
4) The idea of "finding" a carcass out in the desert is pretty much laughable to residents. April temps out there would be hitting the 90s (F). Maybe higher. In August 110 is common. Dead flesh doesn't last out there. Likewise the sheer amount of scavangers makes the survival of anything dead unlikely. The vultures an coyotes would make short work of anything out there.
5) Navigation in this area is VERY difficult. We are talking a "needle meets haystack" situation. Even a huge carcass would be almost impossible to find again.
Combine these, and you have a situation where many people would be fine with a report of some strange creature being killed by some cowboys. Nobody would be keen on looking for the carcass, as finding it would be unlikely. And wandering around the desert back then on horseback was done only for good reason (ie: travel, or the quest for silver). So nobody would look.
The real mystery is this "photograph" that allegedly was run in the
Epitaph . The paper says it never ran. But interstingly many people say it DID. Some even claim that they saw it!
Human memory is obviously somewhat malleable.