Hi Theophil~ "Buffalo" is plural as well as singular, one of those strange English words like "deer", which is also singular and plural. It is true that "buffalos" or alternately, "buffaloes", can be used as a plural but it would sound odd here to the native ear.

Dear One, Buffalo is okay here. I believe here it is used in a generic sense, buffalo in general. It's just how it it used.
We would say cats and dogs and cows and so on. This is something you just learn as you grow up. No one teaches it to us. It's good you asked this usage, for this is an exception to the usual rules.

I didn't even think about it as I used the word buffalo.

Of course, now you know. I am guessing in other languages, this would not be the case.