No, we do not consider Bitcoin to be centralized, but everything here is about the extent to which decentralization takes place in a system.
Many of us know that Bitcoin has several weaknesses related to its pure PoW approach, for instance today we observe the increasing centralization of miners (e.g. Chinese pools). In addition to that, the most common way people exchange cryptos today make them completely dependent on exchange operators such as MtGox and btc-e - we consider that this way should not be centralized in order to avoid making mistakes of the past.
Bitcoin Atom attempts to solve both of the aforementioned problems by bringing a hybrid consensus approach, on-chain atomic swaps via HTLCs and their faster off-chain lightning analogs.
Thanks for the answer. I must admit it makes sense. I've heard about MtGox although I wasn't involved in crypto back then. I wish you good luck devs, seems to me your project can make bitcoin better.