I am not sure how it got updated in your case. But travelling via land, I-94 gets updated only once you re-enter US or if you have paper based I-94 which you have to turn to CBSA office during Canada entry. There is no CBP office at exit, you directly reach CBSA.
Last time when I traveled in 2018, my I-94 did not get updated when I entered Canada, it only got updated once I re-entered US.
Here is the reference from official site:
https://i94.cbp.dhs.gov/I94/#/home
Its on the home page (right side at the bottom).
How do I report my departure if I enter via air and depart via land?
If you have a paper form I-94 and depart by land, you can turn the form into Canadian Border Services Agency (CBSA) upon entry into Canada or to CBP at the port of entry prior to entering Mexico. If you received an electronic I-94 upon arrival by air or sea and depart via land, your departure may not be recorded accurately. A departure will be recorded if you depart via land and re-enter the United States prior to the expiration date stamped in your passport. If you are not a resident of Canada or Mexico and you receive an electronic I-94 and depart via land, but do not re-enter the United States prior to the expiration date stamped on your passport, you may want to travel with evidence of your departure into Canada or Mexico. Evidence of departure can include, but is not limited to, entry stamps in a passport, transportation tickets, pay stubs and/or other receipts. A traveler can request an entry stamp from CBSA when entering Canada or from the InstitutoNacional de Migracion (INM) when entering Mexico.