Chickenboy2004's comment is correct and stall_fest's first guess is also correct. The plural of any Pokémon's name is the same as a addressing a single Pokémon.
"Look at all those Snorlax!" - stall_fest
It's like how some animals in real life that are in groups are addressed like that, except there're all like that in this case.
(idk if listing these are necessary but whatever) Here are some examples: The plural of moose is moose, the plural sheep is sheep, etc.
Source: Experience (and watching the anime over the past few years)