"Biometrics" is an interesting term in the world of immigration, as it has often come to mean something somewhat non-intuitive.
Many countries include a step called "biometrics" as a part of the application process for a visa. In some cases this would consist of simply having your fingerprints and photo taken during the visa application interview. However in many cases - especially when there is no in-person interview required - the "biometrics" step is a separate requirement that generally entails visiting a specific location that may be either a government run facility for the country you're visiting (eg, a consulate), but is more commonly a 3rd party location approved by the government to confirm your identity and collect your biometrics.
For example, if you are applying for most Canadian visas you will need to carry out "Biometrics" at one of the locations listed on this page.
Canada explicitly exempts visitors entering the country using an eTA from having to go through this "biometrics" step in order to obtain their eTA.
On arrival in Canada by air (and potentially also by land depending on the situation), most travelers are required to have their fingerprints taken - regardless of whether they are entering using a visa or an eTA, and regardless of whether they carried out the previous "biometrics" step or not.
For passengers where Canada already has fingerprint/biometric data (people who had this data collected during visa application, or people who have visited Canada before) these fingerprints can be used to confirm the person biometric data matches that which is already on file from the previous collection.
For travelers that have not had their biometric data collected previous (eg, first time eTA visitors), this data is saved for comparison on future entries, as well as potentially used determine if the passenger has been previously known to the government under a different name/passport.
So yes, your conclusion is correct. (The "small airport" exception you mentioned isn't necessarily correct - even then you can be made provide fingerprints if required).