What’s the difference between an I-94 card and a visa?
The I-94 is the little piece of paper given to people on entry. It usually has printed on it the date you entered, the type of status you have, and the date that status (or “stay”) expires.
The visa is issued by a US consulate and is stamped into your passport. It controls only your entry into the United States, not your stay.
It is not uncommon to be given a stay that exceeds your visa. You could enter on the last day of your visa and still receive a stay for several months or more.
By the same token, if you have a visa that is good for ten years (common for a B-2), that doesn’t mean you are still in status once the I-94 expires.