I think it's slander because he does not know how many hours NYT spent on making it
You're confusing the legal concept of "slander" with the concept of "perhaps being wrong". For extra irony, by your definition of slander, you're guilty of it simply by accusing this guy of being guilty of it.
edit: Whoops, by posting this I too am guilty of slander by your definition.
| Anyhow it's an unfair comparison because
| NYT actually had to come up with this idea,
| he just had to replicate it.
No it's not. It could be worded better, but the gist is:
The NYT spend a bunch of time and money to create
Snow Fall. Using this product (scrollkit), you can
create the same thing in about an hour. Call now!
Operators are standing by.
I think it's slander because he does not know how many hours NYT spent on making it, he could be totally wrong yet he is stating it as fact.
Anyhow it's an unfair comparison because NYT actually had to come up with this idea, he just had to replicate it.