> But I don't believe this app is using any actual seeding mechanisms of IPFS from a user perspective
I'm not sure what you mean here. Any user can "seed" any IPFS file they want, they don't need anything from this service.
> in which case it would be no different than a centralised solution
A distributed solution with N=1 isn't the same as a centralized solution. The difference is that distributed solutions can easily increase N, but centralized solutions can't. In this case, you can distribute the file from as many nodes as you control, which makes this service much better than a centralized solution.
> Also, when you use this app, you aren't doing this through an IPFS node to then be able to seed it
Sure, but you can use something like www.eternum.io (or just run your own IPFS node) to fix that. If you don't want to do either, of course you won't have any of the advantages. It's like saying "cars aren't better than couches, they aren't much more comfortable and they don't run if you don't start the engine".