I don't see how their software can be compromised unless they were lying about how are the private keys generated and them being non custodial.
Atomic wallet is closed source. Anything could be hiding in the code, not just from them being actively malicious but also from a rogue employee sneaking something in, a malicious third party sneaking something in, someone compromising their app store log ins to upload a malicious app, or even just plain incompetence.
I am also reminded of the Copay wallet hack several years ago. Copay had a dependency on a specific JavaScript library which was no longer maintained. A malicious third party obtained control of this library, merged a malicious update, and it was pulled in to Copay updates without anyone realizing.
Just another in the long list of reasons to never use closed source wallets.
On top of that, Atomic wallet is owned is owned by Binance which historically has few questionable behavior.
Are you confusing them with Trust wallet? I didn't think Atomic was also owned by Binance?