It’s not that mmcli or qmicli selected that APN, none of those tools would do that.
Your modem is configured to use a specific APN during the LTE registration process, and this happens before you attempt to connect the modem with the user-provided (NetworkManager-provided) APN. This APN used during registration is the one given in the “initial LTE bearer settings”.
In MM git master, you can change these settings with mmcli --3gpp-set-initial-eps-bearer-settings=["key=value,..."] for QMI modems like yours. What this command will do is check which is the 3GPP profile configured to be used during initial attach, and then modify it. In most cases the profile configured for initial attach is the first one, as in your case, and so what you did solved the problem in the same way as we would with the --3gpp-set-initial-eps-bearer-settings operation.
BTW, that fast.t-mobile.com APN was possibly already configured in the module itself, e.g. maybe via carrier configuration or something.