What does bitcoin.org mean when they say about Coldcard Wallet "the final software was not built deterministically like Bitcoin Core"?
Some security sensitive pieces of software like Tor, Debian and Bitcoin use deterministic builds to increase the safety of binaries for end users. Typically a piece of software will be built from source code by a maintainer, signed by them, and then uploaded to a repository. Small differences in the setup of the machine compiling the software, timestamps, and random values in the output mean that every time it is compiled the output is likely to be unique.
Deterministic builds replace this with a system called Gitian that produces identical binary output no matter who produces the binaries or when, allowing many people to independently compile the software and come to the same end result.
Deteminstic builds protect against:

Malicious software on the maintainers machine changing the behavior of the software, injecting a backdoor or other code
A single maintainer acting maliciously and altering the software
An innocent maintainer being accused of having made modifications they did not

The ColdCard product not being built deterministically means that even though the project is open source, you have no way of verifying that the binaries provided by the company completely match the source code.